Apache :: Could not determine fully qualified domain name

Error message:

apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName


Is preety much self-explanatory

Add this
ServerName localhost

In your server configuration file.

Apache :: VirtualHost overlap on port

Errors like


[warn] _default_ VirtualHost overlap on port 443, the first has precedence

are caused because the virtualhosts are not named.

(The same applies for any other port, for example 80)

Add this in your apache configuration file

NameVirtualHost *:443

In Ubuntu server, Linux, that configuration is actually located in the ports.conf file in /etc/apache2.


NameVirtualHost *:80
NameVirtualHost *:443


Listen 80

MySQL not starting when restoring files in /var/lib/mysql

If you get errors like:


120226  1:54:14 [Note] Plugin 'FEDERATED' is disabled.
120226  1:54:14  InnoDB: Initializing buffer pool, size = 8.0M
120226  1:54:14  InnoDB: Completed initialization of buffer pool
120226  1:54:15  InnoDB: Started; log sequence number 0 44233
120226  1:54:15 [ERROR] Event Scheduler: Failed to open table mysql.event
120226  1:54:15 [ERROR] Event Scheduler: Error while loading from disk.
120226  1:54:15 [Note] Event Scheduler: Purging the queue. 0 events
120226  1:54:15 [ERROR] Aborting


120226  1:54:15  InnoDB: Starting shutdown...
120226  1:54:20  InnoDB: Shutdown completed; log sequence number 0 44233
120226  1:54:20 [Note] mysqld: Shutdown complete

or

120226  1:59:18 [Note] Plugin 'FEDERATED' is disabled.

mysqld: Can't find file: './mysql/plugin.frm' (errno: 13)

120226  1:59:18 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.

120226  1:59:18  InnoDB: Initializing buffer pool, size = 8.0M

120226  1:59:18  InnoDB: Completed initialization of buffer pool

120226  1:59:18  InnoDB: Started; log sequence number 0 44233

120226  1:59:18 [ERROR] mysqld: Can't find file: './mysql/host.frm' (errno: 13)

120226  1:59:18 [ERROR] Fatal error: Can't open and lock privilege tables: Can't find file: './mysql/host.frm' (errno: 13)

You need to check the file permissions.

The user and group is mysql:mysql

File permissions are rw for user and group (660)

Solution

chown mysql:mysql -R /var/lib/mysql

chmod 660 -R /var/lib/mysql

Linux/Ubuntu :: pure-ftpd does not allow login to user with /usr/sbin/nologin shell

Expectations:
You have created a user with /usr/sbin/nologin shell (ftp-only user) in Linux/Ubuntu.
If you SSH to the box with this username and password it should not work.
If you FTP to the box with this username and password it should.

Symptoms:
Pure-ftpd does not permit login if the shell is set to /bin/false or /usr/sbin/nologin.
If you change the shell to /bin/bash it works.


Connected to localhost.
220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
220-You are user number 2 of 50 allowed.
220-Local time is now 17:53. Server port: 21.
220-This is a private system - No anonymous login
220-IPv6 connections are also welcome on this server.
220 You will be disconnected after 15 minutes of inactivity.
Name (localhost:root): ftponly
331 User ftponly OK. Password required
Password:
530 Login authentication failed
Login failed.
Remote system type is UNIX.
Using binary mode to transfer files.

Solution:

You need to add the nologin or false shell to the file /etc/shells.

root@box:/# cat /etc/shells

# /etc/shells: valid login shells

/bin/csh

/bin/sh

/usr/bin/es

/usr/bin/ksh

/bin/ksh

/usr/bin/rc

/usr/bin/tcsh

/bin/tcsh

/usr/bin/esh

/bin/dash

/bin/bash

/bin/rbash

/usr/bin/screen

/bin/false

/usr/sbin/nologin

Configuring repcached service on Debian/Ubuntu

Repcached is a slightly modified version of memcached, that supports replication of data between two repcached nodes.

Let's say you've read all about these two and you know the benefits of replication and why this article could be useful to you.

One example of why replicated memcache could be useful are replicated PHP sessions between servers.

If you want to configure that PHP sessions are stored in memcache's memory, you need to edit these settings in /etc/php5/apache2/php.ini:

session.save_handler = memcache
session.save_path = "tcp://IP_OF_REPCACHE_1:11311, tcp://IP_OF_REPCACHE_2:11311"

and these optional settings in /etc/php5/apache2/conf.d /memcache.ini:

memcache.maxratio=0
memcache.allow_failover=1

memcache.allow_failover setting is used if one of the servers becomes unreachable, so there is an automatic failover.
Read more about configuring PHP sessions in memcached here.

Now, let's set up repcached to start on boot and System V init scripts, so you can easly start and stop the daemon with the service command.

Steps described here imitate memcached's default configuration in great detail, so you shoud set up memcached before repcached.

sudo apt-get install memcached

Obtain, configure, compile and install repcached. There is a dependancy with libevent-dev for repcached.

sudo apt-get install libevent-dev
tar xvf memcached-1.2.8-repcached-2.2.tar 
cd memcached-1.2.8-repcached-2.2/
./configure --enable-replication
make
make install

(Read this if it won't compile)

At this point you have two installations of memcached. Default memcached that came from apt packages, which is installed in /usr/bin/memcached and repcached, that installed itself in /usr/local/bin/memcached, leaving the original memcached intact.

Now that we have both versions installed, we can copy memcached's default settings and init script and modify them to use repcached. This way you can quickly switch between versions. I would even recommend using default ports (just remember to firewall them!) Arguments are saved in /etc/memcached.conf, so we will create /etc/repcached.conf

See example here.

Note that the only differences with memcached.conf is the name (repcached) and two extra arguments: -x for the server IP and -X for replication port.

Memcached has an enable/disable config in /etc/default so you can quickly switch between daemons or disable them. We will copy this as well.

cp /etc/default/memcached /etc/default/repcached
vi /etc/default/repcached

Change the line to: ENABLE_REPCACHED=yes, and then edit /etc/default/memcached

vi /etc/default/memcached

and disable it, by changing the line to ENABLE_MEMCACHED=no.

Now let's move on to init scripts.

cd /etc/init.d
cp memcached repcached

Edit the file /etc/init.d/repcached.

Here is my example.

Again, we didn't change much, mostly changed from memcached to repcached, but note that the actual start-up of the service happens in this file: /usr/share/memcached/scripts/start-repcached which doesn't exist yet, so we will copy and edit it.

cp /usr/share/memcached/scripts/start-memcached /usr/share/memcached/scripts/start-repcached

File contents or /usr/share/memcached/scripts/start-repcached

Setting up repcached to start at boot

We need to be sure that /etc/init.d/repcached is executable. If you copied it from memcached, everything should be OK, but if init's not recognising the repcached service, you need to chmod +x /etc/init.d/repcached

After you've run update-rc.d command in the terminal it will create shortcuts in rc?.d files which are read at boot.

update-rc.d repcached defaults

For more information on update-rc.d, click here.

You have successfully configured repcached as a service and to start on boot.

To start/stop repcached use

service repcached start
service repcached stop

Try to run repcached by hand at first with the configuration you provided in /etc/repcached.conf.
In my example it's this:
/usr/local/bin/memcached -m 64 -p 11211 -u memcache -X 11212 -x 22.163.130.33

After installing repcached on another machine I've found out that the default user for memcached is nobody, not memcache, so please always check the differences from the default memcache config with the repcached config you've modified or copied from here.

Kill a zombie process

Well, yes, everybody knows that zombie processes can't be killed, as they're already dead. That's all very well documented and repeated so many times, and the solution to this would be to: "kill the parent process".

Since killing the parent process makes init the parent of the zombie process which can kill zombies, if the real parent can't.

My problem was - how to get the parent process? That's not written anywhere! Why not? Is it so hard?

After some research it turns out it isn't.

You can get the parent process id (PPID) with the -o parameter in 'ps' command:

# ps auxo ppid | grep Z

You know what 'grep Z' does, don't you? It prints only the processes in the Zombie state.

Well when you get the ppid, the solution to zombie killing or reaping is simple.

Just kill -9 the ppid.

I hope this article saves someone from the midnight frustration on why the machine just won't start any new processes, even if CPU load and memory usage are near zero.