Admin Apache CentOS Python Raspberry Pi Web Site Technologies

Traffic shaping on linux – an exploration


I have always been somewhat agog at the idea of limiting bandwidth on my linux servers. Users complain about slow web sites and you want to try it for yourself, slowing your connection down to meet the parameters of their slower connection. More recently I happened on librespeed, an alternative to, where you can run both server and client. But in order to avoid transferring too much data and monopolizing the whole line, I wanted to actually put in some bandwidth throttling. I began an exploration of available methods to achieve this and found some satisfactory approaches that are readily available on Redhat-type linuxes.

bandwidth throttling, bandwidth rate limiting, bandwidth classes – these are all synonyms for what is most commonly called traffic shaping.

What doesn’t work so well

I think it’s important to start with the walls that I hit.


I stumbled on cgroups first. The man page starts in a promising way

cgroup - control group based traffic control filter

Then after you research it you see that support was enabled for cgroups in linux kernels already long ago. And there is version 1 and 2. And only version 1 supports bandwidth limits. But if you’re just a mid-level linux person such as myself, it is confusing and unclear how to take advantage of cgroup. My current conclusion is that it is more a subsystem designed for use by systemctl. In fact if you’ve ever looked at a status, for instance of crond, you see a mention of a cgroup:

sudo systemctl status crond
? crond.service - Command Scheduler
Loaded: loaded (/usr/lib/systemd/system/crond.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2021-08-09 15:44:24 EDT; 5 days ago
Main PID: 1193 (crond)
Tasks: 1 (limit: 11278)
Memory: 2.1M
CGroup: /system.slice/crond.service
mq1193 /usr/sbin/crond -n

I don’t claim to know what it all means, but there it is. Some nice abilities to schedule and allocate finite resources, at a very high level.

So I get the impression that no one really uses cgroups to do traffic shaping.

apache web server to the rescue – not

Since I was mostly interested in my librespeed server and controlling its bandwidth during testing, I wondered if the apache web server has this capability built-in. Essentially, it does! There is the module mod_ratelimit. So, quest over, and let the implementation begin! Except not so fast. In fact I did enable that module. And I set it up on my librespeed server. It kind of works, but mostly, not really, and nothing like its documented design.


    SetOutputFilter RATE_LIMIT
    SetEnv rate-limit 400 
    SetEnv rate-initial-burst 512

That’s their example section. I have no interest in such low limits and tried various values from 4000 to 12000. I only got two different actual rates from librespeed out of all those various configurations. I could either get 83 Mbps or around 162 Mbps. And that’s it. Merely having any statement whatsoever starts limiting to one of these strange values. With the statement commented out I was getting around 300 Mbps. So I got rate-limiting, but not what I was seeking and with almost no control.

So the apache config approach was a bust for me.


There are some linux programs that are perhaps promoted too heavily? Within a minute of posting my first draft of this someone comes along and suggests trickle. Well, on CentOS yum search trickle gives no results. My other OS was SLES v 15 and I similarly got no results. So I’m not enamored with trickle.

tc – now that looks promising

Then I discovered tc – traffic control. That sounds like just the thing. I had to search around a bit on one of my OSes to find the appropriate package, but I found it. On CentOS/Redhat/Fedora the package is iproute-tc. On SLES v15 it was iproute2. On FreeBSD I haven’t figured it out yet.

But it looks unwieldy to use, frankly. Not, as they say, user-friendly.

tcconfig + tc – perfect together

Then I stumbled onto tcconfig, a python wrapper for tc that provides convenient utilities and examples. It’s available, assuming you’ve already installed python, through pip or pip3, depending on how you’ve installed python. Something like

$ sudo pip3 install tcconfig

I love the available settings for tcset – just the kinds of things I would have dreamed up on my own. I wanted to limit download speeds, and only on the web server running on port 443, and noly from a specific subnet. You can do all that! My tcset command went something like this:

$ cd /usr/local/bin; sudo ./tcset eth0 --direction outgoing --src-port 443 --rate 150Mbps --network

$ sudo ./tcshow eth0

"eth0": {
"outgoing": {
"src-port=443, dst-network=, protocol=ip": {
"filter_id": "800::800",
"rate": "150Mbps"
"incoming": {}

More importantly – does it work? Yes, it works beautifully. I run a librespeed cli with three concurrent streams against my AWS server thusly configured and I get around 149 Mbps. Every time.

Note that things are opposite of what you first think of. When I want to restrict download speeds from a server but am imposing traffic shaping on the server (as opposed to on the client machine), from its perspective that is upload traffic! And port 443 is the source port, not the destination port!

Raspberry Pi example

I’m going to try regular librespeed tests on my home RPi which is cabled to my router to do the Internet monitoring. So I’m trying

$ sudo tcset eth0 --direction incoming --rate 100Mbps
$ sudo tcset eth0 --direction outgoing --rate 9Mbps --add

This reflects the reality of the asymmetric rate you typically get from a home Internet connection. tcshow looks a bit peculiar however:

"eth0": {
"outgoing": {
"protocol=ip": {
"filter_id": "800::800",
"delay": "274.9s",
"delay-distro": "274.9s",
"rate": "9Mbps"
"incoming": {
"protocol=ip": {
"filter_id": "800::800",
"delay": "274.9s",
"delay-distro": "274.9s",
"rate": "100Mbps"
Results on the RPi

Despite the strange delay-distro appearing in the tcshow output, the results are perfect. Here are my librespeed results, running against my own private AWS server:

Time is Sat 21 Aug 16:17:23 EDT 2021
Ping: 20 ms Jitter: 1 ms
Download rate: 100.01 Mbps
Upload rate: 9.48 Mbps


Problems creep in on RPi

I swear I had it all working. This blog post is the proof. Now I’ve rebooted my RPi and that tcset command above gives the result Illegal instruction. Still trying to figure that one out!

March, 2022 update. My RPi had other issues. I’ve re-imaged the micro SD card and all is good once again. I set traffic shaping policies as shown in this post.

Conclusion about tcconfig

It’s clear tcset is just giving you a nice interface to tc, but sometimes that’s all you need to not sweat the details and start getting productive.

Possible issue – missing kernel module

On one of my servers (the CentOS 8 one), I had to do a

$ sudo yum install kernel-modules-extra

$ sudo modprobe sch_netem

before I could get tcconfig to really work.

To do list

Make the tc settings permanent.

Verify tc + tcconfig work on a Raspberry Pi. (tc is definitely available for RPi.)


We have found a pretty nice and effective way to do traffic shaping on linux systems. The best tool is tc and the best wrapper for it is tcconfig.

References and related

Librespeed is a great alternative for hard-code linux types who love command line and being in full control of both ends of a speed test. I describe it here.

tcconfig’s project page on PyPi.

Power cycling one’s cable modem automatically via an attached RPi. I refer to this blog post specifically because I intend to expand that RPi to also do periodic, automated speedtesting of my home braodband connection, with traffic shaping in place if all goes well (as it seems to thus far).

Bandwidth management and “queueing discipline” in all its gory detail is explained in this post, including example raw tc commands. I haven’t digested it yet but it may represent a way for me to get my RPi working again without a re-image:

Admin Apache CentOS Linux Security

Trying to upgrade WordPress brings a thicket of problems

Wordpress tells me to upgrade to version 5.4. But when I try it says nope, your version of php is too old. Now admittedly, I’m running on an ancient CentOS server, now at version 6.10, which I set up back in 2012 I believe.

I’m pretty comfortable with CentOS so I wanted to continue with it, but just on a newer version at Amazon. I don’t like being taken advantage of, so I also wanted to avoid those outfits which charge by the hour for providing CentOS, which should really be free. Those costs can really add up.

Lots of travails setting up my AWS image, and then…

I managed to find a CentOS amongst the community images. I chose centos-8-minimal-install-201909262151 (ami-01b3337aae1959300).

OK. Brand new CentOS 8 image, 8.1.1911 after patching it, which will be supported for 10 years. Surely it has the latest and greatest??

Well, I’m not so sure…

If only I had known

I really wish I had seen this post earlier. It would have been really, really helpful:

But I didn’t see it until after I had done all the work below the hard way. Oh well.

When I install php I get version 7.2.11. WordPress is telling me I need a minimum of php version 7.3. If i download the latest php, it tells me to download the latest apache. So I do. Version 2.4.43. I also install gcc, anticipating some compiling in my future…

But apache won’t even configure:

httpd-2.4.43]$ ./configure --enable-so
checking for chosen layout... Apache
checking for working mkdir -p... yes
checking for grep that handles long lines and -e... /usr/bin/grep
checking for egrep... /usr/bin/grep -E
checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking target system type... x86_64-pc-linux-gnu
configure: Configuring Apache Portable Runtime library...
checking for APR... no
configure: error: APR not found.  Please read the documentation.
  --with-apr=PATH         prefix for installed APR or the full path to
  --with-apr-util=PATH    prefix for installed APU or the full path to
(apr-util configure)
checking for APR... no
configure: error: APR could not be located. Please use the --with-apr option.
 ./configure --with-apr=/usr/local/apr
-D_GNU_SOURCE   -I/usr/local/src/apr-util-1.6.1/include -I/usr/local/src/apr-util-1.6.1/include/private  -I/usr/local/apr/include/apr-1    -o xml/apr_xml.lo -c xml/apr_xml.c && touch xml/apr_xml.lo
xml/apr_xml.c:35:10: fatal error: expat.h: No such file or directory
compilation terminated.
make[1]: *** [/usr/local/src/apr-util-1.6.1/build/ xml/apr_xml.lo] Error 1

So I install expat header files:
$ yum install expat-devel
And then the make of apr-util goes through. Not sure this is the right approach or not yet, however.

So following php’s advice, I have:
$ ./configure –enable-so

checking for chosen layout... Apache
checking for pcre-config... false
configure: error: pcre-config for libpcre not found. PCRE is required and available from

So I install pcre-devel:
$ yum install pcre-devel
Now the apache configure goes through, but the make does not work:

/usr/local/apr/build-1/libtool --silent --mode=link gcc  -g -O2 -pthread         -o htpasswd  htpasswd.lo passwd_common.lo       /usr/local/apr/lib/ /usr/local/apr/lib/ -lrt -lcrypt -lpthread -ldl -lcrypt
/usr/local/apr/lib/ undefined reference to `XML_GetErrorCode'
/usr/local/apr/lib/ undefined reference to `XML_SetEntityDeclHandler'
/usr/local/apr/lib/ undefined reference to `XML_ParserCreate'
/usr/local/apr/lib/ undefined reference to `XML_SetCharacterDataHandler'
/usr/local/apr/lib/ undefined reference to `XML_ParserFree'
/usr/local/apr/lib/ undefined reference to `XML_SetUserData'
/usr/local/apr/lib/ undefined reference to `XML_StopParser'
/usr/local/apr/lib/ undefined reference to `XML_Parse'
/usr/local/apr/lib/ undefined reference to `XML_ErrorString'
/usr/local/apr/lib/ undefined reference to `XML_SetElementHandler'
collect2: error: ld returned 1 exit status
make[2]: *** [Makefile:48: htpasswd] Error 1

So I try configure or apr-util with expat built-in.

$ ./configure –with-expat=builtin –with-apr=/usr/local/apr

But when I do the make of apr-util I now get this error:

/usr/local/apr/build-1/libtool: line 7475: cd: builtin/lib: No such file or directory
libtool:   error: cannot determine absolute directory name of 'builtin/lib'
make[1]: *** [Makefile:93:] Error 1
make[1]: Leaving directory '/usr/local/src/apr-util-1.6.1'
make: *** [/usr/local/src/apr-util-1.6.1/build/ all-recursive] Error 1

From what I read this new error occurs due to having –expat-built-in! So now what? So I get rid of that in my configure statement for apr-util. For some reason, apr-util goes through and compiles. And so I try this for compiling apache24:

$ ./configure –enable-so –with-apr=/usr/local/apr

And then I make it. And for some reason, now it goes through. I doubt it will work, however… it kind of does work.

It threw the files into /usr/local/apache2, where there is a bin directory containing apachectl. I can launch apachectl start, and then access a default page on port 80. Not bad so far…

I still need to tie in php however.

I just wing it and try

$ ./configure –with-apxs2=/usr/local/apache2/bin/apxs –with-mysql

Hey, maybe for once their instructions will work. Nope.

configure: error: Package requirements (libxml-2.0 >= 2.7.6) were not met:

Package 'libxml-2.0', required by 'virtual:world', not found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

So I guess I need to install libxml2-devel:

$ yum install libxm2-devel

Looks like I get past that error. Now it’s on to this one:

configure: error: Package requirements (sqlite3 > 3.7.4) were not met:

So I install sqlite-devel:
$ yum install sqlite-devel
Now my configure almost goes through, except, as I suspected, that was a nonsense argument:

configure: WARNING: unrecognized options: --with-mysql

It’s not there when you look for it! Why the heck did they – – give an example with exactly that?? Annoying. So I leave it out. It goes through. Run make. It takes a long time to compile php! And this server is pretty fast. It’s slower than apache or anything else I’ve compiled.

But eventually the compile finished. It added a LoadModule statement to the apache httpd.conf file. And, after I associated files with php extension to the php handler, a test file seemed to work. So php is beginning to work. Not at all sure about the mysql tie-in, however. In fact see further down below where I confirm my fears that there is no MySQL support when PHP is compiled this way.

Is running SSL asking too much?
Apparently, yes. I don’t think my apache24 has SSL support built-in:

Invalid command 'SSLCipherSuite', perhaps misspelled or defined by a module not included in the server configuration

So I try
$ ./configure –enable-so –with-apr=/usr/local/apr –enable-ssl

Not good…

checking for OpenSSL... checking for user-provided OpenSSL base directory... none
checking for OpenSSL version >= 0.9.8a... FAILED
configure: WARNING: OpenSSL version is too old
checking whether to enable mod_ssl... configure: error: mod_ssl has been requested but can not be built due to prerequisite failures

Where is it pulling that old version of openssl? Cause when I do this:

$ openssl version

OpenSSL 1.1.1c FIPS  28 May 2019

That’s not that old…

I also noticed this error:

configure: WARNING: Your APR does not include SSL/EVP support. To enable it: configure --with-crypto

So maybe I will re-compile APR with that argument.

Nope. APR doesn’t even have that argument. But apr-uil does. I’ll try that.

Not so good:

configure: error: Crypto was requested but no crypto library could be enabled; specify the location of a crypto library using --with-openssl, --with-nss, and/or --with-commoncrypto.

I give up. maybe it was a false alarm. I’ll try to ignore it.

So I install openssl-devel:

$ yum install openssl-devel

Then I try to configure apache24 thusly:

$ ./configure –enable-so –with-apr=/usr/local/apr –enable-ssl

This time at least the configure goes through – no ssl-related errors.

I needed to add the Loadmodule statement by hand to httpd.conf since that file was already there from my previous build and so did not get that statement after my re-build with ssl support:

LoadModule ssl_module   modules/

Next error please
Now I have this error:

AH00526: Syntax error on line 92 of /usr/local/apache2/conf/extra/drjohns.conf:
SSLSessionCache: 'shmcb' session cache not supported (known names: ). Maybe you need to load the appropriate socache module (mod_socache_shmcb?).

I want results. So I just comment out the lines that talk about SSL Cache and anything to do with SSL cache.

And…it starts…and…it is listening on both ports 80 and 443 and…it is running SSL. So I think i cracked the SSL issue.

Switch focus to Mysql
I didn’t bother to find mysql. I believe people now use mariadb. So I installed the system one with a yum install mariadb. I became root and learned the version with a select version();

| version()       |
| 10.3.17-MariaDB |
1 row in set (0.000 sec)

Is that recent enough? Yes! For once we skate by comfortably. The WordPress instructions say:

MySQL 5.6 or MariaDB 10.1 or greater

I setup apache. I try to access wordpress setup but instead get this message:

You don't have permission to access this resource.

every page I try gives this error.

The apache error log says:

client denied by server configuration: /usr/local/apache2/htdocs/

Not sure where that’s coming from. I thought I supplied my own documentroot statements, etc.

I threw in a Require all granted within the Directory statement and that seemed to help.

PHP/MySQL communication issue surfaces
Next problem is that PHP wasn’t compiled correctly it seems:

Your PHP installation appears to be missing the MySQL extension which is required by WordPress.

So I’ll try to re-do it. This time I am trying these arguments to configure:
$ ./configure ‐‐with-apxs2=/usr/local/apache2/bin/apxs ‐‐with-mysqli

Well, I’m not so sure this worked. Trying to setup WordPress, I access wp-config.php and only get:

Error establishing a database connection

This is roll up your sleeves time. It’s clear we are getting no breaks. I looked into installing PhpMyAdmin, but then I would neeed composer, which may depend on other things, so I lost interest in that rabbit hole. So I decide to simplify the problem. The suggested test is to write a php program like this, which I do, calling it tst2.php:

$servername = "localhost";
$username = "username";
$password = "password";
// Create connection
$conn = mysqli_connect($servername, $username, $password);
// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
echo "Connected successfully";

Run it:
$ php tst2.php
and get:

PHP Warning:  mysqli_connect(): (HY000/2002): No such file or directory in /web/drjohns/blog/tst2.php on line 7
Warning: mysqli_connect(): (HY000/2002): No such file or directory in /web/drjohns/blog/tst2.php on line 7

Some quick research tells me that php does not know where the file mysql.sock is to be found. I search for it:

$ sudo find / ‐name mysql.sock

and it comes back as


So…the prescription is to update a couple things in pph.ini, which has been put into /usr/local/lib in my case because I compiled php with mostly default values. I add the locatipon of the mysql.sock file in two places for good measure:

pdo_mysql.default_socket = /var/lib/mysql/mysql.sock
mysqli.default_socket = /var/lib/mysql/mysql.sock

And then my little test program goes through!

Connected successfully

Install WordPress
I begin to install WordPress, creating an initial user and so on. When I go back in I get a directory listing in place of the index.php. So I call index.php by hand and get a worisome error:

Fatal error: Uncaught Error: Call to undefined function gzinflate() in /web/drjohns/blog/wp-includes/class-requests.php:947 Stack trace: #0 /web/drjohns/blog/wp-includes/class-requests.php(886): Requests::compatible_gzinflate('\xA5\x92\xCDn\x830\f\x80\xDF\xC5g\x08\xD5\xD6\xEE...'

I should have compiled php with zlib is what I determine it means… zlib and zlib-devel packages are on my system so this should be straightforward.

More arguments for php compiling
OK. Let’s be sensible and try to reproduce what I had done in 2017 to compile php instead of finding an resolving mistakes one at a time.

$ ./configure –with-apxs2=/usr/local/apache2/bin/apxs –with-mysqli –disable-cgi –with-zlib –with-gettext –with-gdbm –with-curl –with-openssl

This gives this new issue:

Package 'libcurl', required by 'virtual:world', not found

I will install libcurl-devel in hopes of making this one go away.

Past that error, and onto this one:

configure: error: DBA: Could not find necessary header file(s).

I’m trying to drop the –with-gdbm and skip that whole DBA thing since the database connection seemed to be working without it. Now I see an openssl problem:

make: *** No rule to make target '/tmp/php-7.4.4/ext/openssl/openssl.c', needed by 'ext/openssl/openssl.lo'.  Stop.

Even if I get rid of openssl I still see a problem when running configure:

gawk: ./build/print_include.awk:1: fatal: cannot open file `ext/zlib/*.h*' for reading (No such file or directory)

Now I can ignore that error because configure exits with 0 status and make, but the make then stops at zlib:

SIGNALS   -c /tmp/php-7.4.4/ext/sqlite3/sqlite3.c -o ext/sqlite3/sqlite3.lo
make: *** No rule to make target '/tmp/php-7.4.4/ext/zlib/zlib.c', needed by 'ext/zlib/zlib.lo'.  Stop.

Reason for above php compilation errors
I figured it out. My bad. I had done a make distclean in addition to a make clean when i was re-starting with a new set of arguments to configure. i saw it somewhere advised on the Internet and didn’t pay much attention, but it seemed like a good idea. But I think what it was doing was wiping out the files in the ext directory, like ext/zlib.

So now I’m starting over, now with php 7.4.5 since they’ve upgraded in the meanwhile! With this configure command line (I figure I probably don’t need gdb):
./configure –with-apxs2=/usr/local/apache2/bin/apxs –with-mysqli –disable-cgi –with-zlib –with-gettext –with-gdbm –with-curl –with-openssl

Well, the php compile went through, however, I can’t seem to access any WordPress pages (all WordPress pages clock). Yet my simplistic database connection test does work. Hmmm. OK. If they come up at all, they come up exceedingly slowly and without correct formatting.

I think I see the reason for that as well. The source of the wp-login.php page (as viewed in a browser window) includes references to former hostnames my server used to have. Of course fetching all those objects times out. And they’re the ones that provide the formatting. At this point I’m not sure where those references came from. Not from the filesystem, so must be in the database as a result of an earlier WordPress install attempt. Amazon keeps changing my IP, you see. I see it is embedded into WordPress. In Settings | general Settings. I’m going to have this problem every time…

What I’m going to do is to create a temporary fictitious name, johnstechtalk, which I will enter in my hosts file on my Windows PC, in Windows\system32\drivers\etc\hosts, and also enter that name in WordPress’s settings. I will update the IP in my hosts file every time it changes while I am playing around. And now there’s even an issue doing this which has always worked so reliably in the past. Well, I found I actually needed to override the IP for in my hosts file. But it seems Firefox has moved on to using DNS over https, so it ignores the hosts file now! i think. Edge still uses it however, thankfully.

So WordPress is basically functioning. I managed to install a few of my fav plugins: Akismet anti-spam, Limit Login Attempts, WP-PostViews. Some of the plugins are so old they actually require ftp. Who runs ftp these days? That’s been considered insecure for many years. But to accommodate I installed vsftpd on my server and ran it, temporarily.

Then Mcafee on my PC decided that is an unsafe site, thank you very much, without any logs or pop-ups. I couldn’t reach that site until I disabled the Mcafee firewall. Makes it hard to learn how to do the next steps of the upgrade.

More WordPress difficulties

WordPress is never satisfied with whatever version you’ve installed. You take the latest and two weeks later it’s demanding you upgrade already. My first upgrade didn’t go so well. Then I installed vsftpd. The upgrade likes to use your local FTP server – at least in my case. so for ftp server I just put in Kind of weird. Even still I get this error:

Downloading update from…

The authenticity of could not be verified as no signature was found.

Unpacking the update…

Could not create directory.

Installation Failed

So I decided it was a permissions problem: my apache was running as user daemon (do a ps -ef to see running processes), while my wordpress blog directory was owned by centos. So I now run apache as user:group centos:centos. In case this helps anyone the apache configurtion commands to do this are:

User centos
Group centos

then I go to my blog directory and run something like:

chown -R centos:centos *
Wordpres Block editor non-functional after the upgrade

When I did the SQL import from my old site, I killed the block editor on my new site! This was disconcerting. That little plus sign just would not show up on new pages, no posts, whatever. So I basically killed wordpress 5.4. So I took a step backwards and started v 5.4 with a clean (empty) database like a fresh install to make sure the block editor works then. It did. Whew! Then I did an RTFM and deactivated my plugins on my old WordPress install before doing the mysql backup. I imported that SQL database, with a very minimal set of plugins activated, and, whew, this time I did not blow away the block editor.

CentOS bogs down

I like my snappy new Centos 8 AMI 80% of the time. But that remaining 20% is very annoying. It freezes. Really bad. I ran a top until the problem happened. Here I’ve caught the problem in action:

top - 16:26:11 up 1 day, 21 min, 2 users, load average: 3.96, 2.93, 5.30
Tasks: 95 total, 1 running, 94 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.1 us, 2.6 sy, 0.0 ni, 0.0 id, 95.8 wa, 0.4 hi, 0.3 si, 0.7 st
MiB Mem : 1827.1 total, 63.4 free, 1709.8 used, 53.9 buff/cache
MiB Swap: 0.0 total, 0.0 free, 0.0 used. 9.1 avail Mem

44 root 20 0 0 0 0 S 1.6 0.0 12:47.94 kswapd0
438 root 0 -20 0 0 0 I 0.5 0.0 1:38.84 kworker/0:1H-kblockd
890 mysql 20 0 1301064 92972 0 S 0.4 5.0 1:26.83 mysqld
5282 centos 20 0 1504524 341188 64 S 0.4 18.2 0:06.06 httpd
5344 root 20 0 345936 1008 0 S 0.4 0.1 0:00.09 sudo
560 root 20 0 93504 6436 3340 S 0.2 0.3 0:02.53 systemd-journal
712 polkitd 20 0 1626824 4996 0 S 0.2 0.3 0:00.15 polkitd
817 root 20 0 598816 4424 0 S 0.2 0.2 0:12.62 NetworkManager
821 root 20 0 634088 14772 0 S 0.2 0.8 0:18.67 tuned
1148 root 20 0 216948 7180 3456 S 0.2 0.4 0:16.74 rsyslogd
2346 john 20 0 273640 776 0 R 0.2 0.0 1:20.73 top
1 root 20 0 178656 4300 0 S 0.0 0.2 0:11.34 systemd

So what jumps out at me is the 95.8% wait time – that ain’t good – an that a process which includes the name swap is at the top of ths list, combined with the fact that exactly 0 swap space is allocated. My linux skills may be 15 years out-of-date, but I think I better allocate some swap space (but why does it need it so badly??). On my old system I think I had done it. I’m a little scared to proceed for fear of blowing up my system.

So if you use and it freezes, just come back in 10 minutes and it’ll probably be running again – this situation tends to self-correct. No one’s perfect.

Making a swap space

I went ahead and created a swap space right on my existing filesystem. I realized it wasn’t too hard once I found these really clear instructions:

Some of the commands are dd to create an empty file, mkswap, swapon and swapon -s to see what it’s doing. And it really, really helped. I think sometimes mariadb needed to swap, and sometimes apache did. My system only has 1.8 GB of memory or so. And the drive is solid state, so it should be kind of fast. Because I used 1.2 GB for swap, I also extended my volume size when I happened upon Amazon’s clear instructions on how you can do that. Who knew? See below for more on that. If I got it right, Amazon also gives you more IO for each GB you add. I’m definitely getting good response after this swap space addition.

An aside about i/o

In the old days I perfected  a way to study i/o using the iostat utility. You can get it by installing the sysstat package. A good command to run is iostat -t -c -m -x 5

Examing these three consecutive lines of output from running that command is very instructional:

Device r/s w/s rMB/s wMB/s rrqm/s wrqm/s %rrqm %wrqm r_await w_await aqu-sz rareq-sz wareq-sz svctm %util
xvda 2226.40 1408.00 9.35 5.54 1.00 0.20 0.04 0.01 2.37 5.00 10.28 4.30 4.03 0.25 90.14

07/04/2020 04:05:36 PM
avg-cpu: %user %nice %system %iowait %steal %idle
1.00 0.00 1.20 48.59 0.60 48.59

Device r/s w/s rMB/s wMB/s rrqm/s wrqm/s %rrqm %wrqm r_await w_await aqu-sz rareq-sz wareq-sz svctm %util
xvda 130.14 1446.51 0.53 5.66 0.60 0.00 0.46 0.00 4.98 8.03 11.47 4.15 4.01 0.32 51.22

07/04/2020 04:05:41 PM
avg-cpu: %user %nice %system %iowait %steal %idle
0.00 0.00 0.00 0.00 0.00 100.00

Device r/s w/s rMB/s wMB/s rrqm/s wrqm/s %rrqm %wrqm r_await w_await aqu-sz rareq-sz wareq-sz svctm %util
xvda 1.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.50 0.00 0.00 2.69 0.00 0.62 0.10

I tooled around in the admin panel (which previously had brought my server to its knees), and you see the %util shot up to 90%, reads per sec over 2000 , writes per second 1400. So, really demanding. It’s clear my server would die if more than a few people were hitting it hard.  And I may need some fine-tuning.


Given all the above problems, you probably never thought I’d pull this off. I worked in fits and starts – mostly when my significant other was away because this stuff is a time suck. But, believe it or not, I got the new apache/openssl/apr/php/mariadb/wordpress/centos/amazon EC2 VPC/drjohnstechtalk-with-new-2020-theme working to my satisfaction. I have to pat myself on the back for that. So I pulled the plug on the old site, which basically means moving the elastic IP over from old centos 6 site to new centos8 AWS instance. Since my site was so old, I had to first convert the elastic IP from type classic to VPC. It was not too obvious, but I got it eventually.

Damn hackers already at it

Look at the access log of your new apache server running your production WordPress. If you see like I did people already trying to log in (POST accesses for …/wp-login.php), which is really annoying because they’re all hackers, at least install the WPS Hide Login plugin and configure a secret login URL. Don’t use the default login.

Meanwhile I’ve decided to freeze out anyone who triess to access wp-login.php because they can only be up to no good. So I created this script which I call

# freeze hackers who probe for wp-login
# DrJ 6/2020
cd $DIR
while /bin/true; do
tail -200 access_log|grep wp-login.php|awk '{print $1}'|sort -u|while read line; do
echo $line
route add -host $line reject
sleep 60

Works great! Just do a netstat -rn to watch your ever-growing list of systems you’ve frozen out.

But xmlrpc is the worst…

Bots which invoke xmlrpc.php are the worst for little servers like mine. They absolutely bring it to its knees. So I’ve just added something similar to the wp-login freeze above, except it catches xmlrpc bots:

# freeze hackers who are doing God knows what to xmlrpc.php
# DrJ 8/2020
cd $DIR
while /bin/true; do
# example offending line:
# - - [21/Aug/2020:08:17:01 -0400] "POST /blog//xmlrpc.php HTTP/1.1" 200 401
tail -100 access_log|grep xmlrpc.php|grep POST|awk '{print $1}'|sort -u|while read line; do
echo $line
route add -host $line reject
sleep 30

I was still dissatisfied with seeing bots hit me up for 30 seconds or so, so I decided heck with it, I’m going to waste their time first. So I added a few lines to xmlrpc.php (I know you shouldn’t do this, but hackers shouldn’t do what they do either):

// DrJ improvements
// just make bot suffer a bit... the freeze out is done by an external script
// end DrJ enhancements

This freeze out trick within xmlrpc.php was only going to work if the bots run single-threaded, that is, they run serially, waiting for one request to finish before sending the next. I’ve been running it for a couple days and have enthusiasitically frozen out a few IPs. I can attest that the bots do indeed run single-threaded. So I typically get two entries in my access file to xmlrpc from a given bot, and then the bot is completely frozen out by the loopback route which gets added.

Mid-term issues discovered months later

Well, I never needed to send emails form my server, until I did. And when I did I found I couldn’t. It used to work from my old server… From reading a bit I see WordPress uses PHP’s built-in mail() function, which has its limits. But my server did not have mailx or postfix packages. So I did a

$ yum install  postfix mailx

$ systemctl enable postfix

$ systemctl start postfix

That still didn’t magically make WordPress mail work, although at that point I could send mail by hand frmo a spoofed address, which is pretty cool, like:

$ mailx -r “” -s “testing email” <<< “Test of a one-line email test. – drJ”

And I got it in my Gmail account from that sender. Cool.

Rather than wasting time debuggin PHP, I saw a promising-looking plug-in, WP Mail SMTP, and installed it. Here is how I configured the important bits:

WP Mail SMTP settings

Another test from WordPress and this time it goes through. Yeah.

Hosting a second WordPress site and Ninja Forms brings it all down

I brushed off my own old notes on hosting more than one WordPress site on my server (it’s nice to be king):

Well, wouldn’t you know my friend’s WordPress site I was trying to host brought my server to its knees. Again. Seems to be a common theme. I was hoping it was merely hackers who’d discovered his new site and injected it with the xmlrpc DOS because that would have been easy to treat. But no, no xmlrpc issues so far according to the access_log file. He uses more of the popular plugins like Elementor and Ninja Forms. Well, that Ninja Forms Dashboard is a killer. Reliably brings my server to a crawl. I even caught it in action from a running top and saw swap was the leading cpu-consuming process. And my 1.2 GB swap file was nearly full. So I created a second, larger swap file of 2 GB and did a swapon for that. Then I decommissioned my older swap file. Did you know you can do a swapoff? Yup. I could see the old one descreasing in size and the new one building up. And now the new one is larger than the old ever could be – 1.4 GB. Now Ninja forms dashboard can be launched. Performance is once again OK.

So…hosting second WordPress site now resolved.

Updating failed. The response is not a valid JSON response.

So then he got that error after enabling permalinks. The causes for this are pretty well documented. We took the standard advice and disabled all plugins. Wihtout permalinks we were fine. With them JSON error. I put the .htaccess file in place. Still no go. So unlike most advice, in my case, where I run my own web server, I must have goofed up the config and not enabled reading of the .htaccess file. Fortunately I had a working example in the form of my own blog site. I put all those apache commands which normally go into .htaccess into the vhost config file. All good.

Increasing EBS filesystem size causes worrisome error

As mentioned above I used some of the filesystem for swap so I wanted to enlarge it.

$ sudo growpart /dev/xvda 1
CHANGED: partition=1 start=2048 old: size=16773120 end=16775168 new: size=25163743,end=25165791
root@ip-10-0-0-181:~/hosting$ sudo lsblk
xvda 202:0 0 12G 0 disk
mqxvda1 202:1 0 12G 0 part /
root@ip-10-0-0-181:~/hosting$ df -k
Filesystem 1K-blocks Used Available Use% Mounted on
devtmpfs 912292 0 912292 0% /dev
tmpfs 935468 0 935468 0% /dev/shm
tmpfs 935468 16800 918668 2% /run
tmpfs 935468 0 935468 0% /sys/fs/cgroup
/dev/xvda1 8376320 3997580 4378740 48% /
tmpfs 187092 0 187092 0% /run/user/0
tmpfs 187092 0 187092 0% /run/user/1001
root@ip-10-0-0-181:~/hosting$ sudo resize2fs /dev/xvda1
resize2fs 1.44.6 (5-Mar-2019)
resize2fs: Bad magic number in super-block while trying to open /dev/xvda1
Couldn't find valid filesystem superblock.

The solution is to use xfs_growfs instead of resize2fs. And that worked!

$ sudo xfs_growfs -d /
meta-data=/dev/xvda1 isize=512 agcount=4, agsize=524160 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1, rmapbt=0
= reflink=1
data = bsize=4096 blocks=2096640, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1
log =internal log bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
data blocks changed from 2096640 to 3145467
root@ip-10-0-0-181:~/hosting$ df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 891M 0 891M 0% /dev
tmpfs 914M 0 914M 0% /dev/shm
tmpfs 914M 17M 898M 2% /run
tmpfs 914M 0 914M 0% /sys/fs/cgroup
/dev/xvda1 12G 3.9G 8.2G 33% /
tmpfs 183M 0 183M 0% /run/user/0
tmpfs 183M 0 183M 0% /run/user/1001
PHP found wanting by WordPress health status

Although my site seems to be humming alnog, now I have to find the more obscure errors. WordPress mentioned my site health has problems.

WordPress site health

I think gd is used for graphics. I haven’t seen any negative results from this, yet. I may leave it be for the time being.

Lets Encrypt certificate renewal stops working

This one is at the bottom because it only manifests itself after a couple months – when the web site certificate either expires or is about to expire. Remember, this is a new server. I was lazy, of course, and just brought over the from the old server, hoping for the best. I didn’t notice any errors at first, but I eventually observed that my certificate was not getting renewed either even though it had only a few days of validity left.

To see what’s going on I ran this command by hand:

“/root/”/ –debug –cron –home “/root/” new-authz error: {"type":"urn:acme:error:badNonce","detail":"JWS has no anti-replay nonce","status": 400}

seemed to be the most important error I noticed. The general suggestion for this is an –upgrade, which I did run. But the nonce error persisted. It tries 20 times then gives up.

— warning: I know enough to get the job done, but not enough to write the code. Proceed at your own risk —

I read some of my old blogs and played with the command

“/root/”/ –issue -d -w /web/drjohns

My Webroot is /web/drjohns by the way. Now at least there was an error I could understand. I saw it trying to access something like

which produced a 404 Not Found error. Note the http and not https. Well, I hadn’t put much energy into setting up my http server. In fact it even has a different webroot. So what I did was to make a symbolic link

ln -s /web/drjohns/.well-known /web/insecure

I re-ran the –issue command and…it worked. Maybe if I had issued a –renew it would not have bothered using the http server at all, but I didn’t see that switch at the time. So in my crontab instead of how you’re supposed to do it, I’m trying it with these two lines:

# Not how you're supposed to do it, but it worked once for me - DrJ 8/16/20
22 2 * * * "/root/"/ --issue -d -w /web/drjohns > /dev/null 2>&1
22 3 16 * * "/root/"/ --update-account --issue -d -w /web/drjohns > /dev/null 2>&1

The update-account is just for good measure so I don’t run into an account expiry problem which I’ve faced in the past. No idea if it’s really needed. Actually my whole approach is a kludge. But it worked. In two months’ time I’ll know if the cron automation also works.

Why kludge it? I could have spent hours and hours trying to get to work as it was intended. I suppose with enough persistence I would have found the root problem.

2021 update. In retrospect

In retrospect, I think I’ll try Amazon Linux next time! I had the opportunity to use it for my job and I have to say it was pretty easy to set up a web server which included php and MariaDB. It feels like it’s based on Redhat, which I’m most familiar with. It doesn’t cost extra. It runs on the same small size on AWS. Oh well.

2022 update

I’m really sick of how far behind Redhat is with their provided software. And since they’ve been taken over by IBM, how they’ve killed CentOS is scandalous. So I’m inclined to go to a Debian-based system for my next go-around, which is much more imminent than I ever expected it to be thanks to the discontinuation of support for CentOS. I asked someone who hosts a lot of WP sites and he said he’d use Ubuntu server 22, PHP 8, MariaDB and NGinx. Boy. Guess I’m way behind. He says performance with PHP 8 is much better. I’ve always used apache but I guess I don’t really rely on it for too many fancy features.

References and related
This blog post is about 1000% better than my own if all you want to do is install WordPress on Centos:

Here is WordPress’s own extended instructions for upgrading. Of course this should be your starting point:

I’ve been following the php instructions:

Before you install WordPress. Requirements and such.

This old article of mine has lots of good tips: Compiling apache 2.4

This is a great article about how Linux systems use swap space and how you can re-configure things:

I found this guide both helpful and informative as well:

Amazon has this clear article on the linux commands you run after you extend an EBS volume. they worked for me:

My Centos 8 AMI is centos-8-minimal-install-201909262151 (ami-01b3337aae1959300)

My old Lets Encrypt article was helpful in straightening out my certificate errors.

Here’s the installation guide for linux.


apache as reverse proxy under SLES

Just got my SLES 12 SP4 server. That’s a type of commercial Linux I needed to set up a secure reverse proxy in a hurry. There’s a lot of suggestions out there. I share what worked for me. The version of apache that is supplied, for the record, is apache 2.4.

The most significant error

[Tue Aug 13 15:26:24.321549 2019] [proxy:warn] [pid 5992] [client] AH01144: No protocol handler was valid for the URL /. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.

The solution
In /etc/sysconfig/apache2 (in SLES this is a macro that sets up apache with the needed loadmodule statements) I needed a statement like the following:

APACHE_MODULES="actions alias auth_basic authn_file authz_host authz_groupfile authz_core authz_user autoindex cgi dir env
expires include log_config mime negotiation setenvif ssl socache_shmcb userdir reqtimeout authn_core proxy proxy_html proxy_http xml2enc"

In my first crack at it I only had mention of modules to include up to proxy. I needed to add proxy_html and proxy_http (I know it doesn’t display correctly in the line above).

In that same file you need a statement like this as well:


The highlights of my virtual host file, based on the ssl template, are:

<VirtualHost *:443>
<Location />
        #  General setup for the virtual host
##      DocumentRoot "/srv/www/htdocs"
        SSLProxyEngine on
        ErrorLog /var/log/apache2/error_log
        TransferLog /var/log/apache2/access_log
        #   SSL Engine Switch:
        #   Enable/Disable SSL for this virtual host.
        SSLEngine on
# from -DrJ 8/19
        SSLProtocol all -SSLv2 -SSLV3 -TLSv1
#SSLCipherSuite HIGH:!aNULL:!MD5:!RC4
        #   You can use per vhost certificates if SNI is supported.
        SSLCertificateFile /etc/apache2/ssl.crt/vhost-example.crt
        SSLCertificateKeyFile /etc/apache2/ssl.key/vhost-example.key
        SSLCertificateChainFile /etc/apache2/ssl.crt/vhost-example-chain.crt
        #   Per-Server Logging:
        #   The home of a custom SSL log file. Use this when you want a
        #   compact non-error SSL logfile on a virtual host basis.
        CustomLog /var/log/apache2/ssl_request_log   ssl_combined

except that I used valid paths to my certificate, key and CA chain files.

Errors you may encounter
$ curl ‐i ‐k https://localhost/

HTTP/1.1 500 Proxy Error
Date: Thu, 15 Aug 2019 19:10:13 GMT
Server: Apache
Content-Length: 442
Connection: close
Content-Type: text/html; charset=iso-8859-1
<title>500 Proxy Error</title>
<h1>Proxy Error</h1>
The proxy server could not handle the request <em><a href="/">GET&nbsp;/</a></em>.<p>
Reason: <strong>Error during SSL Handshake with remote server</strong></p><p />
<p>Additionally, a 500 Internal Server Error
error was encountered while trying to use an ErrorDocument to handle the request.</p>

I traced this error to the fact that initially I did not tell apache to ignore certificate name and other related mismatches. So inserting these directives cured that problem:

SSLProxyVerify none
SSLProxyCheckPeerCN off
SSLProxyCheckPeerName off
SSLProxyCheckPeerExpire off

This is discussed in

I finally got past the SSL errors but then I still had a 404 error and an xml2enc error.

When I ran a service apache2 status I saw this:

Aug 15 16:09:31 lusytp008850388 start_apache2[28539]: [Thu Aug 15 16:09:31.879604 2019] [proxy_html:notice] [pid 28539] AH01425: I18n support in mod_proxy_html requires mod_xml2enc. Without it, non-ASCII characters in proxied pages are likely to display incorrectly.

Not certain whether this was important or not, I simply decided to heed the advice so that’s when I added xml2enc to the list of modules to enable in /etc/sysconfig/apache2:

APACHE_MODLUES=actions alias auth...proxy proxy_html proxy_http xml2enc"
HTTP/1.1 404 Not Found

And that was when I put in a URI that worked just fine if I entered it directly in a browser hitting the web server.

I had a hunch that this could occur if the web server was finicky and insisted on being addressed by a certain name. So originally I had statements like this:


I changed it to


except in place of I put in what I felt the web site operators would have used – the known working alias for direct access to this web site. Of course I first made sure that my apache server could resolve to, which it could.

And, voila, no more 404 error!

Redirects going to the backend server name rather than the public hostname

This was my bad. I actually had in my ProxyPassReverse statement


That’s just not right. And it caused public Internet users to get redirects (the Location HTTP response header) to the private back-end server hostname, which of course they could not resolve or reach. Once I re-read how this was supposed to work and corrected it to

ProxyPassReverse ,

it was all good.

An SSL reverse proxy to an SSL back-end web server was set up under SLES 12 SP4, using TLS 1.2 and apache 2.4.23, in other words, pretty current stuff.

References and related
Compiling apache2.4

Admin Apache Hosting Service Web Site Technologies

Server Name Indication and what it means for those with only a single IP address

Sometimes everything is there in place, ready to be used, but you just have to either mistakenly try it, or learn it works by reading about it, because it may be counter-intuitive. Such is the case with Server Name Indication. I thought I knew enough about https to “know” that you can only have one key/certificate for a single IP address. That CERT can be a SAN (subject alternative name) CERT covering multiple names, but you only get one shot at getting your certificate right. Or so I thought. Turns out I was dead wrong.

Some details
Well, SNI guess is a protocol extension to https. You know I always wondered why in proxy server logs it was able to log the domain name? How would it know that if the http protocol conversation is all encrypted? Maybe it’s SNI at work.

Who supports it?
Since this is an extension it has to be supported by both server and browser. It is. Apache24 supports it. IE, Firefox and Chrome support it. Even my venerable curl supports it! What does not support it, right out of the box, is openssl. The openssl s_client command fetches a site’s certificate, but as I found the hard way, you need to add the -servername switch to tell it which certificate you want to examine, i.e., to force it to use SNI.

This is mainly used by big hosting companies so they can easily and flexibly cram lots of web sites onto a single IP, but us small-time self-hosted sites benefit as well. I host a few sites for friends after all.

Testing methodology
This is pretty simple. I have a couple different virtual servers. I set each up with a completely different certificate in my apache virtual server setups. Then I accessed them by name like usual. Each showed me their own, proper, certificate. That’s it! So this is more than theoretical for me. I’ve already begun to use it.

Enterprise usage
F5 BigIP supports this protocol as well, of course. This article describes how to set it up. But it looks limited to only one server name per certificate, which will be inadequate if there are SAN certificates.

https using Server Name Indication allows to run multiple virtual servers, each with its own unique certificate, on a single IP address.

References and related
I get my certificates for free using the interface to Let’s Encrypt
I’ve written some about apache 2.4 in this post
I don’t think Server Name Indication is explained very well anywhere that I’ve seen. The best dewscription I’ve found is that F5 Devcentral article:
RFC 4366 is the spec describing Server Name Indication.
My favorite openssl commands are listed in this blog post.
SNI is considered insecure because the hostname is sent in plaintext. encrypted SNI is the proposal to address that. Here’s a good write-up about that:

Apache Raspberry Pi

Automating guest wireless access for monitoring purposes with Raspberry Pi

I decided to monitor guest wireless access to the Internet using a Raspberry Pi. By that I mean a basic, binary, is it working now or not response. The back end is a Cisco wireless LAN Controller (WLC). Like most such systems there is no WiFi password, but your connection is extremely limited until you authenticate to the WLC login page in a browser. Further, this particular system is configured to only permit usage for up to four hours, after which another authentication is required to continue. The system is pretty reliable overall, but there are lots of pieces involved and I decided it would be nice to be the first to know if it isn’t working. And it’d be nice to put one of my spare Raspberry Pi’s to work in this semi-official capacity.

The details
Let’s cut to the chase. This is what my crontab file looks like:

# added for drj4guest WiFi testing - DrJ 4/26/17
# this line should keep us authenticating...
* * * * * curl -d `cat /home/pi/data` > /dev/null 2>&1
# and this is what we actually touch, where we have a separate monitor looking for it...every 2 minutes
*/2 * * * * curl`perl -e 'print time;'` > /dev/null 2>&1

For this to work I need accurate time on the Raspberry Pi. By default it was in the wrong timezone – UTC instead of EDT – and it had anyway drifted by quite a few seconds. I describe how to fix this all up in this post.

Let’s break this down. The WiFi is known as drj4guest, hence some of the naming conventions you see.

Here is the contents of the file data in /home/pi:


So I meticulously reverse engineered all the fields the login form sends over and figured out what it is doing.

In the data file I put my assigned WiFi login username, john (replace it with yours) and my password, which also needs to be replaced with an appropriate value for your situation.

Then I decided to run an attempted authentication every one minute, while running the query to my web server every two minutes. That is what the */2 field does in my crontab. That way I will always have authenticated first, even when my four hours has run out.

I like that this also tests the authentication that has been set up, as this could also be the cause of a failure.

Meanwhile my web server log gets entries like this one every two minutes: - - [26/Apr/2017:15:12:02 -0400] "GET /raspberrypidrj4guest?1493233922 HTTP/1.1" 404 219 "-" "curl/7.26.0"

On the webserver
On the webserver being accessed by the Ras Pi I have this Perl script:

# check if Raspberry Pi on the DrJ guest WiFi is phoning home
# - DrJ 4/26/17
# to test good to error transition,
# call with a very small maxDiff, such as 0!
use Getopt::Std;
getopts('m:d'); # maximum allowed time difference
$maxDiff = $opt_m;
$DEBUG = 1 if $opt_d;
unless (defined($maxDiff)) {
$monitorName = 'Raspberry Pi phone home';
# access line looks like:
# - - [02/Feb/2013:22:00:02 -0500] "GET /raspberrypidrj4guest?136456789 HTTP/1.1" 200 455 "-" "curl/7.26.0"
$magicString = "raspberrypidrj4guest";
$accessLog = "/var/log/apache202/access.log";
# pick up timestamp in access file
$piTime = `grep $magicString $accessLog|tail -1|cut -d\? -f2|cut -d' ' -f1`;
$curTime = time();
$date = `date`;
# your PID file is somewhere else. It tells us when Apache was started.
# you could comment out these next lines just to get started with the program
$PID = "/var/run/";
($atime,$mtime,$ctime) = (stat($PID))[8,9,10];
$diff = $curTime - $piTime;
if ($curTime - $ctime < $maxDiff) {
  print "Apache hasn't been running long enough yet to look for something in the log file. Maybe next time\n";
print "magicString, accessLog, piTime, curTime, diff: $magicString, $accessLog, $piTime, $curTime, $diff\n" if $DEBUG;
print "accessLog stat. atime, mtime, ctime: $atime,$mtime,$ctime\n" if $DEBUG;
print "Freshness: $diff s\n";
sub usage {
  print "usage: $0 -m <maxDiff (seconds)> [-d (debug)]\n";

It’s designed to be run by SiteScope as a script monitor. You would run it by hand like this:

> ./ ‐m 300

Freshness: 35 s

If that Freshness time grows too large then the Ras Pi hasn’t been phoning home and you – presumably – have a problem somewhere. /var/log/apache202 happens to be where I have my apache access file on that system.

We showed how to set up a Raspberry Pi to monitor Guest WiFi access on a Cisco Wireless LAN Controller, even though the accounts have to re-authenticated every four hours.

References and related
In the consumer space I do something closely related. I use a Ras Pi at home to monitor whether my Internet connection at home is working. The same phone home concept is used.

Admin Apache Network Technologies Security

drjohnstechtalk now uses HTTP Strict Transport Security, HSTS

I was reading about a kind of amazingly thorough exploit which could be done using a Raspberry Pi zero. Physical access is required, but the scope of what this guy has figured out and put together is really amazing.

Reading the description I decided is a good exercise in making sure I understand the underlying technologies. One was admittedly something I hadn’t seen before: DNS re-binding. That got me to reading about DNS re-binding, and that got me to looking at defenses against DNS rebinding.

HSTS to the rescue
Since in DNS rebinding you may have either a MITM (man in the middle) or a web site impersonated by a hacker, one defense against it is to use HTTPS. (The hacker will not have access to a web site’s private key and therefore has no way to fake a certificate). But what they can do is redirect users from HTTPS to HTTP, where no certificate is required.

HSTS is designed to make that move tip off the user by complaining to the user. Upon first visit the user gets a cookie that says this site should be https. Subsequent visits then are enforced by the user’s browser that the site accessed must be HTTPS.

drjohnstechtalk update
Two years ago I switched the default way I run my blog web site from HTTP to HTTPS due to the encryption offered by HTTPS, and the fact that search engines penalize HTTP sites.

It seems a natural progression in this age of increasing security awareness to up the ante and now also run HSTS. For me this was easy. Since I run my own apache server I simply needed to add the appropriate HTTP Response header to my server responses.

This is done within the virtual server section of the apache configuration like so:

# Guarantee HTTPS for 1/2 Year including Sub Domains  - DrJ 11/22/16
# see
    Header always set Strict-Transport-Security "max-age=15811200; includeSubDomains; preload"

Of course this requires that the apache mod_headers is included.

I test it form a linux server like this:

$ curl ‐i ‐k ‐s|head ‐15

HTTP/1.1 200 OK
Date: Tue, 22 Nov 2016 20:30:56 GMT
Server: Apache/2
Strict-Transport-Security: max-age=15811200; includeSubDomains
Vary: Cookie,Accept-Encoding
X-Powered-By: PHP/5.4.43
Last-Modified: Tue, 22 Nov 2016 20:30:58 GMT
Transfer-Encoding: chunked
Content-Type: text/html; charset=UTF-8
<!DOCTYPE html>
<html lang="en-US">
<meta charset="UTF-8" />

See that new header Strict-Transport-Security: max-age=15811200; includeSubDomains; preload? That’s the result of what we did. But unless we put that preload at the end it doesn’t verify!


References and related
drjohnstechtalk is now encrypted – blog posting from 2014
This site has a good description of the requirements for a proper HSTS implementation, and I see that I missed something!
You can’t run https without a certificate. I soon will be using the free certificates offered by Let’s Encrypt. Here’s my write-up.

Admin Apache CentOS Network Technologies Security Web Site Technologies

Idea for free web server certificates: Let’s Encrypt

I’ve written various articles about SSL. I just came across a way to get your certificates for free, But their thing is to automate certificate management. I think you have to set up the whole automated certificate management environment just to get one of their free certificates. So that’s a little unfortunate, but I may try it and write up my experience with it in this blog (Update: I did it!). Stay tuned.

Short duration certificates
I recently happened upon a site that uses one of these certificates and was surprised to see that it expires in 90 days. All the certificate I’ve ever bought are valid for at least a year, sometimes two or three. But Let’s Encrypt has a whole page justifying their short certificates which kind of makes sense. It forces you to adopt their automation processes for renewal because it will be too burdensome for site admins to constantly renew these certificates by hand the way they used to.

November 2016 update
Since posting this article I have worked with a hosting firm a little bit. I was surprised by how easily he could get for one of “my” domain names. Apparently all it took was that Let’s Encrypt could verify that he owned the IP address which my domain name resolved to. That’s different from the usual way of verification where the whois registration of the domain gets queried. That never happened here! I think by now the Let’s Encrypt CA, IdenTrust Commercial Root CA 1, is accepted by the major browsers.

Here’s a picture that shows one of these certificates which was just issued November, 2016 with its short expiration.


My own experience in getting a certificate
I studied the ACME protocol a little bit. It’s complicated. Nothing’s easy these days! So you need a program to help you implement it. I went with over Certbot because it is much more lightweight – works through bash shell. Certbot wanted to update about 40 packages on my system, which really seems like overkill.

I’m very excited about how easy it was to get my first certificate from letsencrypt! Worked first time. I made sure the account I ran this command from had write access to the HTMLroot (the “webroot”) because an authentication challenge occurs to prove that I administer that web server:

$ ‐‐issue ‐d ‐w /web/drj

[Wed Nov 30 08:55:54 EST 2016] Registering account
[Wed Nov 30 08:55:56 EST 2016] Registered
[Wed Nov 30 08:55:57 EST 2016] Update success.
[Wed Nov 30 08:55:57 EST 2016] Creating domain key
[Wed Nov 30 08:55:57 EST 2016] Single domain=''
[Wed Nov 30 08:55:57 EST 2016] Getting domain auth token for each domain
[Wed Nov 30 08:55:57 EST 2016] Getting webroot for domain=''
[Wed Nov 30 08:55:57 EST 2016] _w='/web/drj'
[Wed Nov 30 08:55:57 EST 2016] Getting new-authz for domain=''
[Wed Nov 30 08:55:58 EST 2016] The new-authz request is ok.
[Wed Nov 30 08:55:58 EST 2016]
[Wed Nov 30 08:56:02 EST 2016] Success
[Wed Nov 30 08:56:02 EST 2016] Verify finished, start to sign.
[Wed Nov 30 08:56:03 EST 2016] Cert success.
[Wed Nov 30 08:56:03 EST 2016] Your cert is in  /home/drj/
[Wed Nov 30 08:56:03 EST 2016] Your cert key is in  /home/drj/
[Wed Nov 30 08:56:04 EST 2016] The intermediate CA cert is in  /home/drj/
[Wed Nov 30 08:56:04 EST 2016] And the full chain certs is there:  /home/drj/

Behind the scenes the authentication resulted in these two accesses to my web server: - - [30/Nov/2016:08:55:59 -0500] "GET /.well-known/acme-challenge/EJlPv9ar7lxvlegqsdlJvsmXMTyagbBsWrh1p-JoHS8 HTTP/1.1" 301 618 "-" "Mozilla/5.0 (compatible; Let's Encrypt validation server; +" - - [30/Nov/2016:08:56:00 -0500] "GET /.well-known/acme-challenge/EJlPv9ar7lxvlegqsdlJvsmXMTyagbBsWrh1p-JoHS8 HTTP/1.1" 200 5725 "" "Mozilla/5.0 (compatible; Let's Encrypt validation server; +" ""

The first was HTTP which I redirect to https while preserving the URL, hence the second request. You see now why I needed write access to the webroot of my web server.

Refine our approach
In the end iI decided to run as root in order to protect the private key from prying eyes. This looked like this:

$ ‐‐issue ‐‐force ‐d ‐w /web/drj ‐‐reloadcmd "service apache24 reload" ‐‐certpath /etc/apache24/certs/drjohnstechtalk.crt ‐‐keypath /etc/apache24/certs/drjohnstechtalk.key ‐‐fullchainpath /etc/apache24/certs/fullchain.cer

What’s a nice feature about is that it remembers parameters you’ve typed by hand and fills them into a single convenient configuration file. So the contents of mine look like this:

Le_CertCreateTimeStr='Fri Dec  2 20:29:30 UTC 2016'
Le_NextRenewTimeStr='Tue Jan 31 20:29:30 UTC 2017'
Le_ReloadCmd='service apache24 reload'

References and related
Examples of using Lets Encrypt with domain (DNS) validation: How I saved $69 a year on certificate cost.
The Let’s Encrypt web site,
When I first switched from http to https: drjohnstechtalk is now an encrypted web site
Let’s Encrypt’s take on those short-lived certificates they issue: Why 90-day certificates script which I used I obtained from this site:
CERTbot client which implements ACME protocol:
IETF ACME draft proposal:

Apache Web Site Technologies

GetSimple CMS – a non-SQL DB content management system

I’ve been looking at GetSimple CMS lately. It allows you to do some basic things so in that sense it’s pretty good.

The details
I know nothing about CMSes, except maybe a tiny bit about WordPress since I use it, but only in a really basic way. I like the idea of a simple CMS however – one that is simple to install and doesn’t even require a database, so this fit the bill.

First problem
My first attempts to use it met with failure. I could create new pages but when I saved them the characters I had typed into the pages were lost, just emptied out. I even went so far as to identify the XML file where these pages are stored and look at the raw xml files. The CDATA that should have contained my typing was blank! At first I was convinced that my version of php was to blame. But I tried different version, 5.3.3, 5.3.17. I still got the problem. So finally I decided that it had to be the fact that I compile my own apache and use somewhat different configuration compared to system defaults. So I switched to a system-supplied apache web server and sure enough, it began to work. Although I would like to believe it’s really something in my configuration, I couldn’t find such a thing and gave up trying. For the record the pages are stored here: <htdocs>/data/pages/<page-name>.xml

Security aspect
I would say this CMS is vulnerable to brute-force attacks. I suggest to randomize the location of the admin login by using the GST-adminlock plugin. You want to have multiple users? The version I used, 3.3.8 accommodates that! It needs just a little fudging to get going. Tie authentication to a back-end database? I doubt that is possible. i did check and it does store the login passwords encrypted. Not sure if there is salt added or not…

I’m especially bad at evaluating plugins. I guess there should be better themes out there because the system-supplied one is so basic. It’s strange that you have to manually get the downloaded plugin onto the server with sftp or some similar tool. Unless I’m missing something, which I probably am.

GetSimple CMS may be good for a 15 – 20 page simple site. It doesn’t need a back-end database, doing all that sort of thing through use of PHP’s XML capabilities. Quite a few plugins exist which extend its functionality. The available documentation is pretty good. Security is adequate and should be made better by the person implementing it. The last thing we need is another way for the bad guys to take over legitimate web sites and inject malicious content.

References and related
Getsimple CMS info is here:
I mentioned compiling my own apache. Usually it all works out for me, but not for use with GetSimple CMS. anyway, here is how I compiled a recent version of apache 2.4.

Admin Apache Hosting Service IT Operational Excellence Linux Web Site Technologies

Scaling your apache to handle more requests

I was running an apache instance very happily with mostly default options until the day came that I noticed it was taking seconds to serve a simple web page – one that it used to serve in 50 ms or so. I eventually rolled up my sleeves to see what could be done about it. It seems that what had changed is that it was being asked to handle more requests than ever before.

The details
But the load average on a 16-core server was only at 2! sar showed no particular problems with either cpu of I/O systems. Both showed plenty of spare capacity. A process count showed about 258 apache processes running.

An Internet search helped me pinpoint the problem. Now bear in mind I use a version of apache I myself compiled, so the file layout looks different from the system-supplied apache, but the ideas are the same. What you need is to increase the number of allowed processes. On my server with its great capacity I scaled up considerably. These settings are in /conf/extra/httpd-mpm.conf in the compiled version. In the system-supplied version on SLES I found the equivalent to be /etc/apache2/server-tuning.conf. To begin with the key section of that file had these values:

<IfModule mpm_prefork_module>
    StartServers             5
    MinSpareServers          5
    MaxSpareServers         10
    MaxRequestWorkers      250
    MaxConnectionsPerChild   0

(The correct section is <IfModule prefork.c> in the system-supplied apache).

I replaced these as follows:

<IfModule mpm_prefork_module>
    StartServers          256
    MinSpareServers        16
    MaxSpareServers       128
    ServerLimit          2048
    MaxClients           2048
    MaxRequestsPerChild  20000

Note that ServerLimit has to be greater than or equal to MaxClients (thank you Apache developers!) or you get an error like this when you start apache:

WARNING: MaxClients of 2048 exceeds ServerLimit value of 256 servers,
 lowering MaxClients to 256.  To increase, please see the ServerLimit

So you make this change, right, stop/start apache and what difference do you see? Probably none whatsoever! Because you probably forgot to uncomment this line in httpd.conf:

#Include conf/extra/httpd-mpm.conf

So remove the # at the beginning of that line and stop/start. If like me you’ve changed the usual diretory where the PID file and lock file get written in your httpd.conf file you may need this additional measure which I had to do in the httpd-mpm.conf file:

<IfModule !mpm_netware_module>
    #PidFile "logs/"
# The accept serialization lock file MUST BE STORED ON A LOCAL DISK.
<IfModule !mpm_winnt_module>
<IfModule !mpm_netware_module>
#LockFile "logs/accept.lock"

In other words I commented out this file’s attempt to place the PID and lock files in a certain place because I have my own way of storing those and it was overwriting my choices!

But with all those changes put together it works much, much better than before and can handle more requests than ever.

In creating a simple benchmark we could easily scale to 400 requests / second, and we didn’t really even try to push it – and this was before we changed any parameters. So why couldn’t 250 or so simultaneous processes handle more real world requests? I believe that if all clients were as fast as our server it could have handled them all. But the clients themselves were sometimes distant (thousands of miles) with slow or lossy connections. Then they need to acknowledge every packet sent by the web server and the web server has to wait around for that, unable to go on to the next client request! Real life is not like laboratory testing. As the waiting around bit requires next-to-no cpu the load average didn’t rise even though we had run up against a limit, the limit was an artificial application-imposed one, not a system-imposed resource constraint.

More analysis, what about threads?

Is this the only or best way to scale up your web server? Probably not. It’s probably the most practical however because you probably didn’t compile it with support for threads. I know I didn’t. Or if you’re using the system-provided package it probably doesn’t support threads. Find your httpd binary. Run this command:

$ ./httpd -l|grep prefork

If it returns:


you have the prefork module and not the worker module and the above approach is what you need to do. To me a more modern approach is to scale by using threads – modern cpus are designed to run threads, which are kind of like light-weight processes. But, oh well. The gatekeepers of apache packages seem stuck in this simple-minded one process per request mindset.

My scaled-up apache is handling more requests than ever. I’ve documented how I increased the total process count.

References and related articles
How I compiled apache 2.4 and ran into (and resolved) a zillion errors seems to be a popular post!
The mystery of why we receive hundreds or even thousands of PAC file requests from each client every day remains unsolved to this day. That’s why we needed to scale up this apache instance – it is serving the PAC file. I first wrote about it three and a half years ago!04

Apache CentOS Hosting Service Web Site Technologies

Compiling Apache 2.4 on CentOS

This is a tale of one thing leading to another. I’ll probably either continue this post or delete it altogether if I find I’m headed down a wrong path.

The details
I suspect that to get better marks for my server’s SSL implementation I probably need apache 2.4. There is an RPM for apache 2.4 but it is almost two years old! So I decided to bite the bullet and compile the darn thing myself. Easier said than done. My current production version is 2.2.15.

Now if you just want to compile a recent version of apache 2.4 then this guide is much, much better than mine: My guide, where I’ve hit just about every conceivable error and powered through, is more for timid folks like me who want to keep their current apache 2.2 running while trying 2.4. In spite of what you read elsewhere this is possible to do, but you need patience and perseverance.

Getting the source is easy enough. Then you configure it:

httpd-2.4.16$ ./configure −−prefix=/usr/local/apache24

checking for chosen layout... Apache
checking for working mkdir -p... yes
checking for grep that handles long lines and -e... /bin/grep
checking for egrep... /bin/grep -E
checking build system type... x86_64-unknown-linux-gnu
checking host system type... x86_64-unknown-linux-gnu
checking target system type... x86_64-unknown-linux-gnu
configure: Configuring Apache Portable Runtime library...
checking for APR... configure: WARNING: APR version 1.4.0 or later is required, found 1.3.9
configure: WARNING: skipped APR at apr-1-config, version not acceptable
configure: error: APR not found.  Please read the documentation.

What version of apr do we have?

$ sudo rpm −qa|grep apr


Drat. No wonder we’re having trouble. Guess we could compile apr ourselves, but perhaps there’s a suitable version out there somewhere we can simply download?

Warning: this approach to apr shown below was a dead end for me. Further down I show a successful approach.

$ sudo yum search apr

Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base:
 * epel:
 * extras:
 * updates:
========================================================== N/S Matched: apr ==========================================================
httpd24-apr-debuginfo.x86_64 : Debug information for package httpd24-apr
httpd24-apr-devel.x86_64 : APR library development kit
httpd24-apr-util-debuginfo.x86_64 : Debug information for package
                                  : httpd24-apr-util
httpd24-apr-util-devel.x86_64 : APR utility library development kit
httpd24-apr-util-ldap.x86_64 : APR utility library LDAP support
httpd24-apr-util-mysql.x86_64 : APR utility library MySQL DBD driver
httpd24-apr-util-nss.x86_64 : APR utility library NSS crytpo support
httpd24-apr-util-odbc.x86_64 : APR utility library ODBC DBD driver
httpd24-apr-util-openssl.x86_64 : APR utility library OpenSSL crytpo support
httpd24-apr-util-pgsql.x86_64 : APR utility library PostgreSQL DBD driver
httpd24-apr-util-sqlite.x86_64 : APR utility library SQLite DBD driver
httpd24-apr.x86_64 : Apache Portable Runtime library
httpd24-apr-util.x86_64 : Apache Portable Runtime Utility library

I singled out the promising looking ones. After all it’s apache 2.4 that’s driving the need for this version so the httpd24 versions of apr should suffice.

So I installed these:

$ sudo yum install httpd24-apr-util.x86_64
$ sudo yum install httpd24-apr-util-devel.x86_64

Now how do we tell the configurator where our new apr package is?

httpd-2.4.16$ ./configure −−help|grep −i apr

  --enable-hook-probes    Enable APR hook probes
  --with-included-apr     Use bundled copies of APR/APR-Util
  --with-apr=PATH         prefix for installed APR or the full path to
  --with-apr-util=PATH    prefix for installed APU or the full path to

The with-apr switch looks promising. Now we guess as to exactly what we should put for the path. Here’s what happens when we guess wrong:

httpd-2.4.16$ ./configure −−with-apr=/opt/rh/httpd24/root/usr/lib64 −−prefix=/usr/local/apache24

checking for chosen layout... Apache
checking for working mkdir -p... yes
checking for grep that handles long lines and -e... /bin/grep
checking for egrep... /bin/grep -E
checking build system type... x86_64-unknown-linux-gnu
checking host system type... x86_64-unknown-linux-gnu
checking target system type... x86_64-unknown-linux-gnu
configure: Configuring Apache Portable Runtime library...
checking for APR... configure: error: the --with-apr parameter is incorrect. It must specify an install prefix, a build directory, or an apr-config file.

I’ll spare you the guesswork. Here is the path correctly specified:

httpd-2.4.16$ ./configure −−with-apr=/opt/rh/httpd24/root/usr −−prefix=/usr/local/apache24

configure: Configuring Apache Portable Runtime Utility library...
checking for APR-util... yes
checking for gcc... gcc
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking how to run the C preprocessor... gcc -E
checking for gcc option to accept ISO C99... -std=gnu99
checking for pcre-config... false
configure: error: pcre-config for libpcre not found. PCRE is required and available from

So we finally got past the apr error and are onto the next one : (. I’ll try to install pcre-devel to see if that helps:

$ sudo yum install pcre-devel.x86_64

Wow! Got lucky that time. That cleared up that error and the configure went all the way through!

Oh, no. It doesn’t compile! It begins to, but it can’t compile export.c:

httpd-2.4.16$ make

gawk -f /usr/local/src/apache24/httpd-2.4.16/build/make_exports.awk `cat export_files` > exports.c
/usr/lib64/apr-1/build/libtool --silent --mode=compile gcc -std=gnu99  -pthread      -DLINUX=2 -D_REENTRANT -D_GNU_SOURCE     -I. -I/usr/local/src/apache24/httpd-2.4.16/os/unix -I/usr/local/src/apache24/httpd-2.4.16/include -I/opt/rh/httpd24/root/usr/include/apr-1 -I/usr/include/apr-1 -I/usr/local/src/apache24/httpd-2.4.16/modules/aaa -I/usr/local/src/apache24/httpd-2.4.16/modules/cache -I/usr/local/src/apache24/httpd-2.4.16/modules/core -I/usr/local/src/apache24/httpd-2.4.16/modules/database -I/usr/local/src/apache24/httpd-2.4.16/modules/filters -I/usr/local/src/apache24/httpd-2.4.16/modules/ldap -I/usr/local/src/apache24/httpd-2.4.16/modules/loggers -I/usr/local/src/apache24/httpd-2.4.16/modules/lua -I/usr/local/src/apache24/httpd-2.4.16/modules/proxy -I/usr/local/src/apache24/httpd-2.4.16/modules/session -I/usr/local/src/apache24/httpd-2.4.16/modules/ssl -I/usr/local/src/apache24/httpd-2.4.16/modules/test -I/usr/local/src/apache24/httpd-2.4.16/server -I/usr/local/src/apache24/httpd-2.4.16/modules/arch/unix -I/usr/local/src/apache24/httpd-2.4.16/modules/dav/main -I/usr/local/src/apache24/httpd-2.4.16/modules/generators -I/usr/local/src/apache24/httpd-2.4.16/modules/mappers  -prefer-non-pic -static -c exports.c && touch exports.lo
exports.c:1244: error: redefinition of ‘ap_hack_apr_allocator_create’
exports.c:198: note: previous definition of ‘ap_hack_apr_allocator_create’ was here
exports.c:1245: error: redefinition of ‘ap_hack_apr_allocator_destroy’
exports.c:199: note: previous definition of ‘ap_hack_apr_allocator_destroy’ was here
exports.c:1246: error: redefinition of ‘ap_hack_apr_allocator_alloc’
exports.c:200: note: previous definition of ‘ap_hack_apr_allocator_alloc’ was here
exports.c:1247: error: redefinition of ‘ap_hack_apr_allocator_free’
exports.c:201: note: previous definition of ‘ap_hack_apr_allocator_free’ was here
exports.c:1248: error: redefinition of ‘ap_hack_apr_allocator_owner_set’

This could be tough! Maybe impossible for me to get past. I’ve never encountered this kind of error. OK. Got it. Not so tough. I had two versions of apr installed – the old one needed by my apache 2.2 and the new one installed as shown above. I didn’t want to completely blow away the old one as I feared that it is dynamically linked by Apache 2.2, so I did the following:

$ cd /usr/lib64; sudo mv apr-1 drjapr-1
– then change to my apache24 root directory and run configure again; then run make

And it went through this time!

Only modules installed
make install however only installed modules, not the httpd binary.

The problem seems related to my original apr libraries. They look like this:

$ sudo rpm −qa|grep ^apr


I tried to move them all to a temporary directory but then the compiler cannot find libtool which is normally supplied by apr-devel.

I considered removing apr-devel, but boy there are so many dependencies that my other packages have on it that I did not feel comfortable doing that. PHP, apache2.2 and a whole lot more depend on it.

End of dead end approach to apr

New approach needed
My new approach is to try to use the APR from apache itself by downloaded the Unix sources for APR and apr-util from Yes, this worked best of all. I even put back all the apr files I had moved in the previous failed effort.

It’s not very clear what they mean by unpacking apr and apr-util in srclib. I created symlinks in my srclib directory such that apr -> apr-1.5.2 and apr-util -> apr-util-1.5.4. For the inexperienced the command format is like in this example:

$ ln −s apr-1.5.2 apr

Of course you first have to download the source tarball to your srclib directory and unpack it:

$ tar zxf apr-1.5.2.tar.gz

It Compiles and Installs
So after all those misfires I finally got a version that compiled and installed in its entirety. That process starts with this configure command:

$ ./configure −−with-included-apr −−prefix=/usr/local/apache24

Then the usual make and sudo make install.

Modules problem
I inherited a configuration that had a mods-avalable and a mods-enabled directory which is how my old apache 2.2 was set up. After tweaking the modules path using the replace command, something like this

$ cd /etc; cp −pr apache2 apache24; cd mods-avalable
$ sudo replace /usr/lib/apache2 /usr/local/apache24 −− *.load

I still could not start my new server:

Starting apache24: httpd: Syntax error on line 203 of /etc/apache24/apache24.conf: Syntax error on line 1 of /etc/apache24/mods-enabled/authz_default.load: Cannot load /usr/local/apache24/modules/ into server: /usr/local/apache24/modules/ cannot open shared object file: No such file or directory

I looked at all my configuration files and don’t see anything that relies on this module so I deleted the reference to it in mods-enabled.

Starting apache24: httpd: Syntax error on line 203 of /etc/apache24/apache24.conf: Syntax error on line 1 of /etc/apache24/mods-enabled/cgi.load: Cannot load /usr/local/apache24/modules/ into server: /usr/local/apache24/modules/ cannot open shared object file: No such file or directory

Now I do like to run CGI programs on occasion so this one can’t be so easily brushed aside. It could be that we should be using instead.

Then it’s onto this error:

Starting apache24: httpd: Syntax error on line 203 of /etc/apache24/apache24.conf: Syntax error on line 1 of /etc/apache24/mods-enabled/php5.load: Cannot load /usr/local/apache24/modules/ into server: /usr/local/apache24/modules/ cannot open shared object file: No such file or directory

I use php so I may have to investigate this one in some detail. simply trying to update the link to where the old resides under apache2.2 brings up this different kind of error:

Starting apache24: httpd: Syntax error on line 203 of /etc/apache24/apache24.conf: Syntax error on line 1 of /etc/apache24/mods-enabled/php5.load: Cannot load /usr/lib/apache2/modules/ into server: /usr/lib/apache2/modules/ undefined symbol: unixd_config

Wow. I’m reading various things and it looks like I’ll now have to compile php5 as well. This is getting hairy. This site, although old, seems to explain it most clearly. And of course I’ve got php 5.3 which you can’t even find source for on the php web site,

So I downloaded php5.4.43, which is the oldest one I could find on the php web site!

To configure it I used this long list of options, some of which are determined by my choices of location for my apache24 files:

$ ./configure ‐‐with‐apxs2=/usr/local/apache24/bin/apxs ‐‐with‐mysql ‐‐prefix=/usr/local/apache24/php5 ‐‐with‐config‐file ‐path=/usr/local/apache24/php5 ‐‐disable‐cgi ‐‐with‐zlib ‐‐with‐gettext ‐‐with‐gdbm ‐‐with‐curl ‐‐with‐openssl

2017 update for php
I finally needed to update some WordPress packages and found my only transport is ftp. I think my command-line compile options for php5 above leave something to be desired. I think I need to add curl and openssl like so:

$ ./configure ‐‐with‐apxs2=/usr/local/apache24/bin/apxs ‐‐with‐mysql ‐‐prefix=/usr/local/apache24/php5 ‐‐with‐config‐file ‐path=/usr/local/apache24/php5 ‐‐disable‐cgi ‐‐with‐zlib ‐‐with‐gettext ‐‐with‐gdbm ‐‐with‐curl ‐‐with‐openssl

but I get these errors:

ext/curl/.libs/interface.o: In function `php_curl_option_url':
/usr/local/src/php5/php-5.4.43/ext/curl/interface.c:180: undefined reference to `core_globals'
ext/curl/.libs/interface.o: In function `_php_curl_setopt':
/usr/local/src/php5/php-5.4.43/ext/curl/interface.c:1821: undefined reference to `core_globals'
/usr/local/src/php5/php-5.4.43/ext/curl/interface.c:1804: undefined reference to `core_globals'
ext/curl/.libs/interface.o: In function `curl_progress':
/usr/local/src/php5/php-5.4.43/ext/curl/interface.c:1113: undefined reference to `executor_globals'
ext/curl/.libs/interface.o: In function `curl_write_header':
/usr/local/src/php5/php-5.4.43/ext/curl/interface.c:1264: undefined reference to `executor_globals'
ext/curl/.libs/interface.o: In function `curl_write':
/usr/local/src/php5/php-5.4.43/ext/curl/interface.c:1038: undefined reference to `executor_globals'
ext/curl/.libs/interface.o: In function `curl_read':
/usr/local/src/php5/php-5.4.43/ext/curl/interface.c:1187: undefined reference to `executor_globals'
ext/curl/.libs/streams.o: In function `php_curl_stream_opener':
/usr/local/src/php5/php-5.4.43/ext/curl/streams.c:320: undefined reference to `file_globals'
/usr/local/src/php5/php-5.4.43/ext/curl/streams.c:406: undefined reference to `core_globals'
/usr/local/src/php5/php-5.4.43/ext/curl/streams.c:414: undefined reference to `core_globals'
ext/curl/.libs/streams.o: In function `on_data_available':
/usr/local/src/php5/php-5.4.43/ext/curl/streams.c:68: undefined reference to `executor_globals'
ext/standard/.libs/info.o: In function `php_info_print_request_uri':
/usr/local/src/php5/php-5.4.43/ext/standard/info.c:97: undefined reference to `sapi_globals'
ext/standard/.libs/info.o: In function `php_print_gpcse_array':
/usr/local/src/php5/php-5.4.43/ext/standard/info.c:213: undefined reference to `executor_globals'
ext/standard/.libs/info.o: In function `php_print_info':
/usr/local/src/php5/php-5.4.43/ext/standard/info.c:918: undefined reference to `executor_globals'
collect2: ld returned 1 exit status
make: *** [sapi/cli/php] Error 1

Here the problem seems to be that since I had already compiled php5 and left it around, it was using the old parts.

You need to do a make clean first! Then it compiles.

Now I’m down to this apache error:

$ sudo service apache24 start

Starting apache24: AH00526: Syntax error on line 55 of /etc/apache24/apache24.conf:
Invalid command 'LockFile', perhaps misspelled or defined by a module not included in the server configuration

I’m going to just try to comment out that pesky Option LockFile…. I’ve found this apache page which is helpful for this upgrade: OK, next error:

Starting apache24: AH00526: Syntax error on line 145 of /etc/apache24/apache24.conf:
Invalid command 'User', perhaps misspelled or defined by a module not included in the server configuration

Here the advice is to load module mod_unixd. I don’t even have anything like that so I’m looking into it now. OK. It’s in the apache24/modules so I just need to load it in. Next error:

Starting apache24: AH00526: Syntax error on line 161 of /etc/apache24/apache24.conf:
Invalid command 'Order', perhaps misspelled or defined by a module not included in the server configuration

Wow. That comes from this pretty standard line:

<Files ~ "^\.ht">
    Order allow,deny
    Deny from all
    Satisfy all

This is a helpful document: So at their recommendation I replaced all that with a

Require all denied

That leads to the next error:

Starting apache24: AH00526: Syntax error on line 166 of /etc/apache24/apache24.conf:
Invalid command 'Require', perhaps misspelled or defined by a module not included in the server configuration

It means Require is not even found. I needed to load some new modules, names authz_code and unixd:

LoadModule authz_core_module /usr/local/apache24/modules/
LoadModule unixd_module /usr/local/apache24/modules/

Next error:

AH00526: Syntax error on line 20 of /etc/apache24/mods-enabled/alias.conf:
Invalid command 'Order', perhaps misspelled or defined by a module not included in the server configuration

so some of my old conf files that I copied over use the old syntax. The alias.conf file looked like this:

Alias /icons/ "/var/www/icons/"
<Directory "/var/www/icons">
    Options Indexes MultiViews
    AllowOverride None
    Order allow,deny
    Allow from all

Again looking at they suggest to replace the Order… and following line with:

Require all granted

Next error:

AH00526: Syntax error on line 3 of /etc/apache24/mods-enabled/deflate.conf:
Invalid command 'AddOutputFilterByType', perhaps misspelled or defined by a module not included in the server configuration

But I was already loading the deflate module which defines AddOutputfilterByType. What I learned is that in apache 2.4 you also need to load mod_filter.

And the next error please:

AH00526: Syntax error on line 43 of /etc/apache24/mods-enabled/ssl.conf:
SSLSessionCache: 'shmcb' session cache not supported (known names: ). Maybe you need to load the appropriate socache module (mod_socache_shmcb?).

That’s in complaint about this line:

SSLSessionCache        shmcb:${APACHE_RUN_DIR}/ssl_scache(512000)

The standard advice for this error is to uncomment this line:

LoadModule socache_shmcb_module modules/

But I don’t have that module!

I guess I chose the wrong options when doing the initial ./configure. See the references for a proper guide that lists some good options.

I’m now trying to configure like this:

$ ./configure −−with-included-apr −−prefix=/usr/local/apache24 −−enable-php5 −−enable-so −−enable-ssl −−with-mpm=prefork

Actually I don’t know if I needed all those options such as enable-ssl. The main thing was that my apache 2.2 mods-available directory didn’t have a mention of My apache 2.4 built with these config options definitely does. so I just need one of these LoadModule statements like this:

LoadModule socache_shmcb_module /usr/local/apache24/modules/

Well we’ve moved six lines down into that config file. I guess that’s progress! because now we’ve made it all the wy to line 49:

AH00526: Syntax error on line 49 of /etc/apache24/mods-enabled/ssl.conf:
Invalid command 'SSLMutex', perhaps misspelled or defined by a module not included in the server configuration

Even apache’s upgrade guide documents this error. It’s caused by a conf file line that looks something like this:

SSLMutex  file:${APACHE_RUN_DIR}/ssl_mutex

and they say – I’m paraphrasing here – just try to comment it out and hope for the best.

Next error:

AH00526: Syntax error on line 9 of /etc/apache24/mods-enabled/status.conf:
Invalid command 'Order', perhaps misspelled or defined by a module not included in the server configuration

Yeah status.conf has

    Order deny,allow
    Deny from all
    Allow from ::1

We’ll try to replace that with this:

Require host ::1

Now it runs through all the configuration OK but doesn’t actually start. I had set up an init.d script and I wasn’t going to go into this but I may have to:

$ sudo service apache24 start

httpd (pid 30896) already running

Remember I am trying to run this while still running the old apache 2.2 server. Process 30896 is the old apache 2.2:

root     30896     1  0 10:05 ?        00:00:00 /usr/sbin/httpd -d /etc/apache2 -f apache2.conf

This results from the byzantine way I set up to launch apache. There is a /etc/sysconfig/apache24 which doesn’t do much other than import environment variable definitions from /etc/apache24/envvars, except I had forgotten to update that path so it pointed to the old /etc/apache2/envvars.

Now it starts! But not without complaint:

Starting apache24: [Thu Aug 06 11:18:04.711658 2015] [core:warn] [pid 22911] AH00117: Ignoring deprecated use of DefaultType in line 178 of /etc/apache24/apache24.conf.
                                                              [  OK  ]

That stems from this line which tries to establish a default MIME type:

DefaultType text/plain

I also notice I cannot really get the status of my new web server:

$ sudo service apache24 status

httpd dead but subsys locked

So stopping/starting doesn’t really work either once it’s started.

What I found is that it seems happier if I have a line in /etc/sysconfig/apache24 which has an explicit PIDFILE defined – I use PIDFILE=/var/run/ – with the same filepath as is mentioned in the apache24.conf file, where I have PidFile ${APACHE_PID_FILE} where APACHE_PID_FILE is taken from my envvars and has the value /var/run/ OK, my setup is very convoluted and probably unique. But the problem is common on CentOS so the main takeway is to have consistent reference to the pidfile filepath in /etc/sysconfig/httpd or whatever you are calling it as in your main config file httpd.conf or whatever you are calling it.

Home page test (I’m running on port 1443 to avoid conflict with my production server):

$ curl −i −k

HTTP/1.1 301 Moved Permanently
Date: Wed, 05 Aug 2015 18:33:19 GMT
Server: Apache/2
X-Powered-By: PHP/5.4.43
Content-Length: 2
Content-Type: text/html

So that looks pretty good.

A simple php test:

$ curl −i −k

Long output. Basically looks right.

OK. What about the opening WordPress page?

$ curl −i −H ‘Host:’ −k

Yes. Big long output. Looks good. I don’t think this proves that the mySQL/php interface is really working however as that page could be cached since I use a pagecache plugin.

Next test I’d like to run is the Qualys SSLLabs test, but it won’t run on port 1443. Maybe the DigiCERT test will. Yes, it does allow it. And I no longer have the BREACH vulnerability.

A few words about a BREACH test
This prompted me to look at why Digicert felt I was vulnerable to BREACH in the first place. I thnk it’s related to serving compressed objects. So I thought of this simple test. Against my apache 2.2 I can run a query like this:

$ curl −i −k −−compress|head −10

Date: Fri, 07 Aug 2015 14:02:48 GMT
Server: Apache/2
X-Powered-By: PHP/5.3.3
Vary: Accept-Encoding
Content-Encoding: gzip
Content-Length: 30414
Content-Type: text/html
<!DOCTYPE html>
<html lang="en-US">

See that Content-Encoding: gzip? Yet the actual content that begins <!DOCTYPE html… is in plain text and plainly not compressed. So I really wasn’t vulnerable to BREACH at all. The server claimed to be compressing the pages it was sendnig to the browser but in reality it wasn’t. For apache 2.4 the behaviour is basically the same except there is no response header Content-Encoding: gzip returned. This is why it passes Digicert’s BREACH test with flying colors.

Moving on
Next test. Swap apache 2.2 for apache 2.4 by changing listening ports 443 for 1443. Then do the SSLlabs test. I now get an A. well, actually I get an A both before and after the swap.

WordPress test
I’m writing this using my new shiny apache 2.4. With regards to WordPress it all seems to feel the same as before. One small thing I’ve noticed is that I don’t get WordPress news any longer:

RSS Error: WP HTTP Error: There are no HTTP transports available which can complete the requested request.

Hopefully there’s nothing more serious.

php.ini missing
If you blindly copied my config options for compiling php then sooner or later (much later in my case) you’ll realize that you have no valid php.ini file! You will see an error like this when the date() function is called:

Warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in

So because I used the config option –with-config-fil
e-path=/usr/local/apache24/php5 I needed to put a php.ini file in that directory and only that directory. For now its contents are:

; DrJ, inspired by - 12/31/14
; Maximum allowed size for uploaded files.
upload_max_filesize = 10M
; Must be greater than or equal to upload_max_filesize
post_max_size = 10M
; You'll need this to avoid errors with the Date function
; Defines the default timezone used by the date functions
date.timezone = America/New_York

Appendix A
mod_ssl error after patching

I have an apache 2.2.21 server on a SLES server. After a system patch (I guess) I realized the apache web server wouldn’t start. It shows this error:

> sudo service apache201 start

Starting httpd (/usr/local/apache2/bin/httpd) httpd: Syntax error on line 54 of /usr/local/apache201/conf/httpd.conf: Cannot load /usr/local/apache201/modules/ into server: /usr/local/apache201/modules/ undefined symbol: ap_map_http_request_error

I had been playing fast and loose and I borrowed the from some other system, I guess. I forget which. In other words, I dropped in by hand a into the directory /usr/lib64/apache2-prefork. I was using those system-supplied modules paired with my compiled apache. All fine until that patch. So I found another frm a different system and tried that one. It worked. Whew. These were both SLES 11 SP 4 systems. The older one (with the that still works) is dated April 18th, 2017. The one with the broken Dec 29thth 2017. That’s from a uname -a.

References and related articles
A proper guide to installing apache 2.4 on CentOS is

Some upgrade issues are covered by apache’s own guide:

Scaling up apache to handle more than a couple hundred simultaneous requests is described in this blog post.

The DigiCERT certificate inspector tool, which is what I was referring to in this post when it comes to scanning for BREACH vulnerabilities, is here.