One of the other threads mentioned that MySQL comes with sample config files you can use.

I decided to try replacing the contents of my my.cnf file with the contents of /usr/share/doc/mysql-server-5.1/examples/my-small.cnf.

I'm using Ubuntu 10.04 LTS by the way.

When I restarted MySQL by issuing the command "sudo service mysql restart", it kind of froze up my terminal (the command never finished I guess), and I got this lovely error on my PHP pages with MySQL queries:

Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

Any idea what might cause this? Here is the my-cnf file I used, and the original config file.

my-small.cnf

# Example MySQL config file for small systems.
#
# This is for a system with little memory (<= 64M) where MySQL is only used
# from time to time and it's important that the mysqld daemon
# doesn't use much resources.
#
# You can copy this file to
# /etc/my.cnf to set global options,
# mysql-data-dir/my.cnf to set server-specific options (in this
# installation this directory is /var/lib/mysql) or
# ~/.my.cnf to set user-specific options.
#
# In this file, you can use all long options that a program supports.
# If you want to know which options a program supports, run the program
# with the "--help" option.

# The following options will be passed to all MySQL clients
[client]
#password   = your_password
port      = 3306
socket      = /var/run/mysqld/mysqld.sock

# Here follows entries for some specific programs

# The MySQL server
[mysqld]
port      = 3306
socket      = /var/run/mysqld/mysqld.sock
skip-locking
key_buffer_size = 16K
max_allowed_packet = 1M
table_open_cache = 4
sort_buffer_size = 64K
read_buffer_size = 256K
read_rnd_buffer_size = 256K
net_buffer_length = 2K
thread_stack = 128K

# Don't listen on a TCP/IP port at all. This can be a security enhancement,
# if all processes that need to connect to mysqld run on the same host.
# All interaction with mysqld must be made via Unix sockets or named pipes.
# Note that using this option without enabling named pipes on Windows
# (using the "enable-named-pipe" option) will render mysqld useless!
# 
#skip-networking
server-id   = 1

# Uncomment the following if you want to log updates
#log-bin=mysql-bin

# binary logging format - mixed recommended
#binlog_format=mixed

# Uncomment the following if you are using InnoDB tables
#innodb_data_home_dir = /var/lib/mysql/
#innodb_data_file_path = ibdata1:10M:autoextend
#innodb_log_group_home_dir = /var/lib/mysql/
# You can set .._buffer_pool_size up to 50 - 80 %
# of RAM but beware of setting memory usage too high
#innodb_buffer_pool_size = 16M
#innodb_additional_mem_pool_size = 2M
# Set .._log_file_size to 25 % of buffer pool size
#innodb_log_file_size = 5M
#innodb_log_buffer_size = 8M
#innodb_flush_log_at_trx_commit = 1
#innodb_lock_wait_timeout = 50

[mysqldump]
quick
max_allowed_packet = 16M

[mysql]
no-auto-rehash
# Remove the next comment character if you are not familiar with SQL
#safe-updates

[myisamchk]
key_buffer_size = 8M
sort_buffer_size = 8M

[mysqlhotcopy]
interactive-timeout

my.cnf (the original config file)

#
# The MySQL database server configuration file.
#
# You can copy this to one of:
# - "/etc/mysql/my.cnf" to set global options,
# - "~/.my.cnf" to set user-specific options.
# 
# One can use all long options that the program supports.
# Run program with --help to get a list of available options and with
# --print-defaults to see which it would actually understand and use.
#
# For explanations see
# http://dev.mysql.com/doc/mysql/en/server-system-variables.html

# This will be passed to all mysql clients
# It has been reported that passwords should be enclosed with ticks/quotes
# escpecially if they contain "#" chars...
# Remember to edit /etc/mysql/debian.cnf when changing the socket location.
[client]
port      = 3306
socket      = /var/run/mysqld/mysqld.sock

# Here is entries for some specific programs
# The following values assume you have at least 32M ram

# This was formally known as [safe_mysqld]. Both versions are currently parsed.
[mysqld_safe]
socket      = /var/run/mysqld/mysqld.sock
nice      = 0

[mysqld]
#
# * Basic Settings
#

#
# * IMPORTANT
#   If you make changes to these settings and your system uses apparmor, you may
#   also need to also adjust /etc/apparmor.d/usr.sbin.mysqld.
#

user      = mysql
socket      = /var/run/mysqld/mysqld.sock
port      = 3306
basedir      = /usr
datadir      = /var/lib/mysql
tmpdir      = /tmp
skip-external-locking
#
# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
bind-address      = 127.0.0.1
#
# * Fine Tuning
#
key_buffer      = 16M
max_allowed_packet   = 16M
thread_stack      = 192K
thread_cache_size       = 8
# This replaces the startup script and checks MyISAM tables if needed
# the first time they are touched
myisam-recover         = BACKUP
#max_connections        = 100
#table_cache            = 64
#thread_concurrency     = 10
#
# * Query Cache Configuration
#
query_cache_limit   = 1M
query_cache_size        = 16M
#
# * Logging and Replication
#
# Both location gets rotated by the cronjob.
# Be aware that this log type is a performance killer.
# As of 5.1 you can enable the log at runtime!
#general_log_file        = /var/log/mysql/mysql.log
#general_log             = 1

log_error                = /var/log/mysql/error.log

# Here you can see queries with especially long duration
#log_slow_queries   = /var/log/mysql/mysql-slow.log
#long_query_time = 2
#log-queries-not-using-indexes
#
# The following can be used as easy to replay backup logs or for replication.
# note: if you are setting up a replication slave, see README.Debian about
#       other settings you may need to change.
#server-id      = 1
#log_bin         = /var/log/mysql/mysql-bin.log
expire_logs_days   = 10
max_binlog_size         = 100M
#binlog_do_db      = include_database_name
#binlog_ignore_db   = include_database_name
#
# * InnoDB
#
# InnoDB is enabled by default with a 10MB datafile in /var/lib/mysql/.
# Read the manual for more InnoDB related options. There are many!
#
# * Security Features
#
# Read the manual, too, if you want chroot!
# chroot = /var/lib/mysql/
#
# For generating SSL certificates I recommend the OpenSSL GUI "tinyca".
#
# ssl-ca=/etc/mysql/cacert.pem
# ssl-cert=/etc/mysql/server-cert.pem
# ssl-key=/etc/mysql/server-key.pem



[mysqldump]
quick
quote-names
max_allowed_packet   = 16M

[mysql]
#no-auto-rehash   # faster start of mysql but no tab completition

[isamchk]
key_buffer      = 16M

#
# * IMPORTANT: Additional settings that can override those from this file!
#   The files must end with '.cnf', otherwise they'll be ignored.
#
!includedir /etc/mysql/conf.d/

MySQL probably stopped and didn't restart....

Try sudo /etc/init.d/mysql status to see if it's running

If it's not, try starting it sudo /etc/init.d/mysql start

If that doesn't work, get your old config file in place and try starting it to at least get you running. I'd suggest making modifications to your config file and restarting mysql instead of just replacing it out right with some file that may or may not work.

I get...

jeff@ubuntu:~$ service mysql start
start: Unable to connect to system bus: Failed to connect to socket /var/run/dbus/system_bus_socket: No such file or directory

jeff@ubuntu:~$ service mysql status
status: Unable to connect to system bus: Failed to connect to socket /var/run/dbus/system_bus_socket: No such file or directory

Looks like you don't have root rights, try using sudo

Ahh, you're right. I did:

jeff@ubuntu:~$ sudo service mysql start
mysql start/running
jeff@ubuntu:~$ sudo service mysql status
mysql start/running

So now it's definitely running, right? That PHP page still gives me the same error though:

Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

I guess the lesson is "don't swap out config files."

Sadly, I did try this on my production server. Luckily, I was smart enough to save my original my.cnf file before changing it so that I could quickly revert to it.