New Zealand Linux

Do your usual install on wordpress, and get it up and running. If you are not sure what that is, download the zip, upload the contents to your website, then point your browser at it to finish the configuration.
Once you have filled out your database information, and sorted themes etc you can then move onto the next step. Do not enable any plugins at this stage, some may be incompatible with multiuser!

Look for the file wp-config.php on your server, you need to edit it and add in one line to it.

define('WP_ALLOW_MULTISITE', true);

Once you have added it, refresh your dashboard and go to Network settings under Tools section. This will give you two Options
* Subdirectories as in http://yourdomain.com/someuser/
* Subdomains as in http://user.yourdomain.com

Most people will want to use subdomains, This will require a wildcard DNS entry however. That means just add an A record of * pointing to the IP of your server, then add in the apache config below before restarting.

ServerAlias *.yourdomain.com

Once you have done this you can go under the SuperUser menu and add a site in.

Some extra wordpress notes:
* make the plugins/themes folder writable by the web server. It needs to be owned by the same user not just chmod 777/666 for some reason on a lot/most systems. This is so it can read/write plugins etc without the FTP details. Using the FTP is a more secure option, however it can be painful and annoying to do.
* Not all plugins are compatible with multiuser
* Security can be a problem, one site gets compromised, all sites may be.

I’m working on servers all day everyday, mostly by SSH. This can be annoying when you switch tabs and then want to go back to another and its timed you out and dead.
A nice quick shortcut to kill that session is to type in ‘~.’ This needs to be on a new line so it wont hurt to press enter beforehand. You will not see it echo on screen, but it will kill the inactive/dead ssh session nicely.

Before you login again, if you are running Linux on your local machine, you can add the following into /etc/ssh/ssh_config

    ServerAliveInterval 5

This will send a packet every 5 seconds to keep the connection alive. Very handy. You can make that longer if you want to use less bandwidth and your servers are setup ok with a longer keep alive.

Once you have logged into your server you can edit the /etc/sshd_config and add in the following

TCPKeepAlive yes
ClientAliveInterval 60

This will keep things ticking over from the server point of view. Once you have added that in , restart the SSHD daemon with /etc/init.d/ssh restart . This will not kill your current SSH session, though it pays to logout and log back in again for it to take effect.

Do remember security, you do not want to leave your local machine alone, unlocked, with a live SSH session running logged in as root on a production server!

Today i had a person who had an interesting problem. They were getting the message ‘disk is full’ despite having plenty of free space. Luckily for him, my first thought was ‘inodes?’
I logged in and checked his inode usage

root@askdev:# df -i
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/xvda1 525312 524844 468 100% /
varrun 65579 27 65552 1% /var/run
varlock 65579 2 65577 1% /var/lock
udev 65579 2696 62883 5% /dev
devshm 65579 1 65578 1% /dev/shm

This shows that all the inodes on the disk itself are full.
I used the following script to determine where the inode usage was most

root@askdev:/# for i in `ls -1A`; do echo “`find $i | sort -u | wc -l` $i”; done | sort -rn | head -5
468388 var
49844 usr
18741 proc
5187 sys
5026 root

I tracked it down to /var/lib/php5/ and all the session files in there.

I used a find to then find any that were older than 10 days

root@askdev:/var/lib/php5# find ./ -type f -mtime +10 | wc -l
111041

High inode usage is usually caused by a massive number of small files. In this case the session files are normally stored somewhere temporary and removed when not in use. Either there could have been a bug in the code not removing them or it was a higher traffic website.

You can delete files older than 10 days if you want with the following command

cd /dir/of/inodes
find ./ -type f -mtime +10 | xargs rm