All posts by nicholas

OS, Web

Speed up WordPress in CentOS7 using caching

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It has recently come to my attention that WordPress has a serious design flaw: it’s trivially easy to execute a denial of service attack against it in its default state. One simply has to hold down F5 to cause the site to slow to a crawl and in many cases crash entirely.

The reason behind this is that every single page request turns into the server parsing PHP code and executing a database call. Holding down F5 initiates hundreds of page view requests, which turn into hundreds of PHP code execution threads (each taking up CPU and memory) and hundreds of database calls. The server becomes quickly overwhelmed and runs out of resources.

The solution to this problem (on CentOS 7 at least) is a combination of php-fpm, zendopcache, APC, varnish and W3 Total Cache. It’s definitely more complicated but it eliminates this problem and massively increases site load times and general responsiveness.

Repositories

To install the required addons we will need to have the epel repository enabled:

yum -y install epel-release

zend-opcache

This caches PHP opcode to greatly speed up PHP code execution. It’s included in later versions of PHP but alas CentOS 7 is stuck on PHP 5.4, which does not include such caching. You have to install it manually. Thanks to this site for the information.

sudo yum -y install php-pecl-zendopcache

apc

This is another kind of of cache – this time for database operations.

sudo yum -y install php-pecl-apcu php-devel gcc
sudo pecl install apc
#accept defaults when prompted

php-fpm

php-fpm is a different way to serve up PHP code. Instead of apache running a module to interpret php code, it will send all php requests to a separate PHP server, optimized for speed. That php server will interpret the code and return the results to your browser.

sudo yum -y install php-fpm
sudo systemctl enable php-fpm

Modify your apache config to forward all php requests to php-fpm. Be sure to modify this to match your site URL setup:

sudo sh -c "echo '
    <LocationMatch \"^/(.*\.php(/.*)?)$\"> 
        ProxyPass fcgi://127.0.0.1:9000/var/www/html/\$1 
    </LocationMatch>' >> /etc/httpd/conf/httpd.conf"

Varnish

Varnish is a reverse proxy server optimized for caching pages. It sits between your visitors and your webserver and caches whatever it can to increase responsiveness and speed. This site pointed me in the right direction for configuring Varnish  in CentOS 7.

sudo yum -y install varnish
sudo systemctl enable varnish

Change apache to listen on port 8080 instead of port 80:

sudo sed -i /etc/httpd/conf/httpd.conf -e 's/Listen 80/&80/'

Change varnish to listen on port 80 instead of port 6081:

sudo sed -i /etc/varnish/varnish.params -e 's/VARNISH_LISTEN_PORT=6081/VARNISH_LISTEN_PORT=80/g'

Now we need to configure Varnish to properly cache wordpress sites. I found the configuration from this site to be the most helpful. I normally include code blocks to copy and paste but the configuration file is pretty big.

Instead, click here for the configuration code, then copy the whole page and paste it into your terminal.

Update 12/28/2016: I’ve updated the varnish configuration code slightly to allow the “purge all caches” button of W3 Total cache to work. Thanks to this site for pointing me in the right direction and this thread for getting me there.

After varnish has been configured, restart your new PHP / caching stack:

sudo systemctl restart httpd varnish php-fpm

Logging

Update: added this section on 11/4/2016

By default varnish does not log its traffic. This means that your apache log will only log things varnish does not cache. We have to configure varnish to log traffic so you don’t lose insight into who is visiting your site.

Update 2/14/2017:  I’ve discovered a better way to do this. The old way is still included below, but you really should use this other way.

New way:

CentOS ships with some systemd scripts for you. You can use them out of the box by simply issuing

systemctl start varnishncsa
systemctl enable varnishncsa

If you are behind a reverse proxy then you will want to tweak the varnishncsa output a bit to reflect x-forwarded-for header values (thanks to this github discussion for the guidance.) Accomplish this by appending a modified log output format string to /lib/systemd/system/varnishncsa.service:

sudo sed -i /lib/systemd/system/varnishncsa.service -e "s/ExecStart.*/& -F \'%%{X-Forwarded-For}i %%l %%u %%t \"%%r\" %%s %%b \"%%{Referer}i\" \"%%{User-agent}i\"\' /g"

Lastly, reload systemd configuration, enable, and start the varnishncsa service:

sudo systemctl daemon-reload
sudo systemctl enable varnishncsa
sudo systemctl start varnishncsa

Old way:

First, enable rc.local

sudo chmod +x /etc/rc.local
sudo systemctl enable rc-local #you can ignore errors here

Next, add this entry to the rc.local file:

sudo sh -c 'echo "varnishncsa -a -w /var/log/varnish/access.log -D -P /var/run/varnishncsa.pid" >> /etc/rc.local'

If your varnish server is behind a reverse proxy (like a web application firewall) then modify the above code slightly (thanks to this site for the information on how to do so)

sudo sh -c "echo varnishncsa -a -F \'%{X-Forwarded-For}i %l %u %t \"%r\" %s %b \"%{Referer}i\" \"%{User-agent}i\"\' -w /var/log/varnish/access.log -D -P /var/run/varnishncsa.pid >> /etc/rc.local"

W3 Total Cache

The improvements above will greatly increase your speed and eliminate the F5 denial of service issue. The last bit to make it even sweeter is to install the W3 Total Cache wordpress plugin. Thanks to this site for the information that pointed me in the right direction.

There are a ton of options in W3 Total cache that are beyond the scope of this tutorial. For our purposes we will enable the following options in the General Settings tab of the plugin:

opcode-database-object

Opcode cache: Opcode:Zend Opcache

Database cache: Check enable, select Opcode: Alternative PHP Cache (APC / APCu)

Object cache: Check enable, select Opcode: Alternative PHP Cache (APC / APCu)

proxy

Reverse Proxy: Check “Enable reverse proxy caching via varnish”
Specify 127.0.0.1 in the varnish servers box. Click save all settings.

Full speed ahead

With all of these pieces into place your site is definitely more complicated, but it is also much faster to load. Enjoy.

Troubleshooting

If you go through all these steps only to see this very non-descriptive message:

File not found

it means you have PHP forwarding to the wrong directory. Modify the LocationMatch section you inserted at the bottom of /etc/httpd/conf/httpd.conf earlier to ensure the correct directory structure is passed for php files.

CLI, OS

Reboot a windows system remotely

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I recently came across the need to reboot my Windows 10 workstation remotely. I couldn’t RDP into the box  – it would stay stuck on the disclaimer splash screen. There was an OK button but it did nothing when clicked.

My solution was to initiate a reboot command from another Windows PC on the same network as my Windows 10 workstation. I figured out how to do so thanks to this article.

To remotely reboot yourself, log onto another Windows box and open up a command shell with an account that has administrative permissions on the machine you want to reboot. Then, issue this command:

shutdown -r -f -m \\<remote machine name> -t 30 -c "<message>"

The above command forces a reboot command (shutdown -r -f) on the remote machine (-m \\machine name), causes a countdown timer for the number of seconds specified (-t 30) and displays a message on the screen (-c “message”).

It solved my issue and was pretty easy to do. Handy.

CLI

Rename files for proper sorting in Linux

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I often come across files than are named 1..9 and then go to 10…99. The problem is many Linux programs begin with 1, then go to 10, etc. The sorting is wrong. Fortunately the rename command comes to our rescue:

rename 's/\d+/sprintf("%05d", $&)/e' *.jpg

Running the above command looks for numbers in the name of JPG files (in the current directory) and renames the file to ensure there are 5 digits in the filename. Now, instead of 1.jpg, your file will be named 00001.jpg. Handy.

Thanks to this forum for the information.

CLI, OS

Updated crouton OpenVPN script

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Updates to Chrome OS have broken the VPN script I had for crouton. I had to tweak a few things including a default route for my VPN server so that broken VPN connections could automatically reconnect.  I had to work around another new security feature:  selinux denying sed the ability to create temp files in /etc. The updated script works well, though… until Google updates ChromeOS again 🙂

See this post for instructions on how to implement the script.

Here it is:

#!/bin/bash

CONF_DIR="DIR_CONTAINING_OVPN_FILE"
CONF_FILE="NAME_OF_OVPN_FILE"
DNS_SERVER="ADDRESS_OF_VPN_DNS_SERVER"
VPN_SERVER=$(cat $CONF_DIR/$CONF_FILE | grep remote | awk '{print $2}')
DEFAULT_GW=$(sudo route | grep default | awk '{print $2}' )

cd "$CONF_DIR"

# Add google DNS on top of current ones, since openvpn command does not do it
sudo cp /etc/resolv.conf /tmp/resolv.conf
sudo sed -i "1s/^/# new DNS\nnameserver $DNS_SERVER\n# old DNS\n/" /tmp/resolv.conf
sudo cp /tmp/resolv.conf /etc/resolv.conf

sudo openvpn --config "$CONF_FILE" --dev tun0

# When ctrl-c is hit remove tun0 and cleanup the DNS
sudo openvpn --rmtun --dev tun0
sudo cp /etc/resolv.conf /tmp/resolv.conf
sudo sed -i '/# new DNS/,/# old DNS/d' /tmp/resolv.conf
sudo cp /tmp/resolv.conf /etc/resolv.conf
trap 2
CLI, OS, Web

Install WordPress on CentOS 7 with SELinux

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I’ve been frustrated lately with the number of tutorials for installing WordPress on CentOS 7 that say to simply turn SELinux off. This is an unacceptable workaround. It’s simply lazy administration. SELinux is not designed to make your job harder (although it can do that pretty well), it’s there to make your system safer.

I have scoured the internet and pieced together bits of information from several sources – mainly here, here, and here to put together a tutorial that walks you through how to install WordPress in CentOS7 while keeping SELinux turned on.

It took a lot of reading to understand SELinux, but once you understand it, it makes a whole lot more sense. Go figure.

Apache

Install required packages:

sudo yum -y install httpd
sudo systemctl enable httpd

Modify apache config to allow mod_rewrite:

sudo sed -i /etc/httpd/conf/httpd.conf -e 's/AllowOverride None/AllowOverride All/g'

Open necessary firewall ports:

sudo firewall-cmd --add-service=http --permanent
sudo systemctl restart firewalld

Start apache:

sudo systemctl start httpd

Navigate to your new site to make sure the testing page comes up.

Update 11/4/2016: If you are behind a reverse proxy such as varnish or a web application firewall, you will want to modify your apache configuration to log x-forwarded-for IPs to make the logs more meaningful:

sudo sed -i /etc/httpd/conf/httpd.conf -e 's/%h/%{X-Forwarded-For}i/g'

MariaDB

Install:

sudo yum -y install mariadb-server mariadb
sudo systemctl enable mariadb

Run initial mysql configuration to set database root password

sudo systemctl start mariadb
sudo mysql_secure_installation

Create a wordpress database and user:

mysql -u root -p 
#enter your mysql root password here
create user wordpress;
create database wordpress;
GRANT ALL PRIVILEGES ON wordpress.* To 'wordpress'@'localhost' IDENTIFIED BY 'password';
quit;

WordPress

Install PHP and restart apache

sudo yum -y install php php-mysql php-gd php-ldap php-odbc php-pear php-xml php-xmlrpc php-mbstring php-snmp php-soap curl
sudo systemctl restart httpd

Configure base wordpress directory

Download, extract, and set permissions for your wordpress installation:

wget https://wordpress.org/latest.zip
sudo unzip latest.zip -d /var/www/html
sudo chown apache:apache -R /var/www/html/wordpress

Optional: Change Apache document root so you don’t need to tack /wordpress at the end of the url:

sudo sed -i /etc/httpd/conf/httpd.conf -e 's/DocumentRoot \"\/var\/www\/html/&\/wordpress/g'
sudo systemctl restart httpd

Configure upload directory

If you want users to upload content, then you will want to assign the http_sys_rw_content_t selinux security context for the wp-uploads directory (create it if it doesn’t exist)

sudo mkdir /var/www/html/wordpress/wp-content/uploads
sudo chown apache:apache /var/www/html/wordpress/wp-content/uploads
sudo semanage fcontext -a -t httpd_sys_rw_content_t "/var/www/html/wordpress/wp-content/uploads(/.*)?"
sudo restorecon -Rv /var/www/html/wordpress/wp-content/uploads

Run the wizard

In order for the wizard to run properly we need to temporarily give the wordpress directory httpd_sys_rw_content_t selinux context

sudo chcon -t httpd_sys_rw_content_t /var/www/html/wordpress/

Now navigate to your new website in a browser and follow the wizard, which will create a wp-config.php file inside the wordpress directory. Once your site is properly set up, restore the original security context for the wordpress directory:

sudo restorecon -v /var/www/html/wordpress/

Success! Everything is working within the proper SELinux contexts.

Troubleshooting

Permission denied when accessing /wordpress

The obvious thing to check is to make sure the directory /var/www/html/wordpress has the ownership set to apache. That didn’t fix my issue, though. Thanks to serverfault I narrowed this down to a selinux permissions issue.  Changing the selinux context to httpd_sys_content_t for the wordpress folder fixed the issue.

sudo semanage fcontext -a -t httpd_sys_content_t /var/www/html/wordpress/
sudo restorecon -v /var/www/html/wordpress/

Sorry, but I can’t write the wp-config.php file.

“You can create the wp-config.php manually and paste the following text into it.”

I had a suspicion that writing files was also a selinux issue. This was confirmed when I decided to tail /var/log/audit/audit.log and found this when the wordpress installer tried to write wp-config.php:

type=AVC msg=audit(1475596102.558:16868): avc: denied { write } for pid=5751 comm="httpd" name="wordpress" dev="dm-0" ino=68494934 scontext=system_u:system_r:httpd_t:s0 tcontext=system_u:object_r:httpd_sys_content_t:s0 tclass=dir
type=SYSCALL msg=audit(1475596102.558:16868): arch=c000003e syscall=21 success=no exit=-13 a0=7f9f4b931478 a1=2 a2=0 a3=1 items=0 ppid=5740 pid=5751 auid=4294967295 uid=48 gid=48 euid=48 suid=48 fsuid=48 egid=48 sgid=48 fsgid=48 tty=(none) ses=4294967295 comm="httpd" exe="/usr/sbin/httpd" subj=system_u:system_r:httpd_t:s0 key=(null)

This led me to find this great explanation from Francis Pereira on how to get wordpress and selinux to peacefully coexist. Also thanks to the excellent Redhat Manual for more information on what to do, combined with this very helpful guide from serverlab.

First, we need to temporarily grant httpd_sys_rw_content_t to the wordpress directory. This is to allow the initial wizard to create the wp-config.php file.

sudo chcon -t httpd_sys_rw_content_t /var/www/html/wordpress/

Now you can run the wizard and it will work properly.

Once your site is set up, restore the context to http_sys_content_t

sudo restorecon -v /var/www/html/wordpress/
CLI

Mountpoint check script

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I wrote a simple script to check to see if a specific mountpoint on a Linux system is still live.  It does this by trying to read a specific file on the share, and if it cannot, write the event to a log, unmount, and then re-mount the folder. The need arose for instances where a file server has been rebooted and the linux system loses the connection to the share. This way it will automatically re-mount.

Modify the variables section as needed and then have a cron job run the script as root at whatever interval you want. Enjoy.

#!/bin/bash
#Script to monitor mount directories to ensure they are properly mounted
#Place a file with the word "mounted" in it inside all mounted directories
#The script will try to read the file and attempt to unmount and remount the folder if it fails to read the file
#Updated 8/30/2016 by Nicholas Jeppson

#---------Variable section------------#

#Place mount folder locations here, separated by space 
#Paths containing spaces need to have quotes around them
LOCATIONS=(/home/njeppson /home/njeppson/Desktop)

#Name of file to try to read
TEST_FILENAME="mountcheck"

#---------End Variable Section--------#
#-----Do not edit below this line-----#

#Read file, if contents don't contain "mounted" then attempt to unmount and re-mount the folder, output attempt to /var/log/mountcheck

for FOLDER in "${LOCATIONS[@]}"; do 
 if [[ $(cat $FOLDER/$TEST_FILENAME) != "mounted" ]]; then
 echo "$(date "+%b %d %T") $(hostname) $FOLDER Not mounted, remounting." >> /var/log/mountcheck 
 umount $FOLDER
 mount $FOLDER
 fi
done
Gaming, OS

Battle.net won’t update after copying from network folder

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I ran into an issue recently where I tried to copy a battle.net game (Heroes of the Storm) from a backup folder on my NAS onto a new computer. Once the copy was completed I couldn’t get battle.net to update the game. It kept failing with error code:

BLZBNTAGT00000840

file update failed for an unknown reason.

After much digging I found this post which mentions it’s due to the fact that the updater apparertly can’t update files with the hidden attribute. The hidden file attribute gets applied by the NAS because the file in question has a dot in front of it in the filename. For some reason the updater can’t touch it.

The fix is to change all files in the game folder to not have the hidden attribute. The easiest way to do this is via the command line. Navigate to the folder of the game you copied over and execute the following:

attrib -H .* /S

Finally, I can copy Blizzard game backups without agonizing over why they won’t patch.

CLI, OS, Web

FreeBSD: allow non-root processes to bind port 80

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In experimenting with FreeNAS jails I wanted to allow a web service to use port 80. Normally 80 is a high order port reserved for root-level processes for security reasons. Since this is a FreeBSD jail and not a full on system I’m not worried about this.

The command to do so is fairly simple (thanks to this page for information)

sysctl net.inet.ip.portrange.reservedhigh=0

The above command is not permanent; to make it so add it to /etc/sysctl.conf:

echo "net.inet.ip.portrange.reservedhigh=0" >> /etc/sysctl.conf
CLI, OS

FreeNAS unable to create jails fix

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I recently got a shiny new FreeNAS Mini appliance. It’s the bee’s knees. Previously I was using a virtualized instance of FreeNAS that has served me admirably for two years now. During the migration I decided to start fresh with the jails configuration I had and deleted the entire jails dataset. This turned out to be a mistake. I suddenly found out that I couldn’t create any jails or plugins. The plugin download would hang for a long time and flash a brief message “Failed to download plugin.” Not helpful.

I tried changing the location of my jails in configuration to no avail. I even tried nuking my FreeNAS config entirely and starting from scratch. The error still happened! Somehow that configuration survived a factory restore.

I finally found this freenas forum entry that pointed me in the right direction. It suggested I use the warden command to delete the plugin jail template completely and re-install it. When I tried to I got this error:

 

[nicholas@freenas ~]$ sudo warden template delete pluginjail
ERROR: Not a ZFS volume: /mnt/storage/jails/.warden-template-pluginjail

It was still trying to install the plugin template in my non-existent dataset. I decided to try re-creating the missing dataset and then running the warden delete command again. Success!

[nicholas@freenas ~]$ sudo zfs create storage/jails/.warden-template-pluginjail
[nicholas@freenas ~]$ sudo warden template delete pluginjail

Once you delete the template jail via warden, you can re-create it in the right place after configuring the correct path in Jails / Configuration. Once you have the right place configured, issue the following:

warden template create -nick pluginjail -tar http://download.freenas.org/jails/9.3/x64/freenas-pluginjail-9.3-RELEASE.tgz

Plugins and jails work again! Success.

CLI

The power of find, grep, and xargs

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Recently I needed to find folders with two different things in the path – mysql and DB. I toyed around with a bunch of options but finally settled on using xargs. I don’t use it much. I should use it more.

The command below takes output from find, greps it twice (thus looking for things that have both terms in them) and then creates a symbolic link of the results.

 find . -type d | grep mysql | grep DB | xargs -n 1 ln -s

This accomplished what I needed quite well. In a huge stash of folders there were a subset that contained both the words mysql and DB in their paths that  I was interested in. Find, grep, and xargs to the rescue.