Ubuntu – the MySQL InnoDB log files stored

All log files are located in /var/log directory. In that directory, there are specific files for each type of logs. For example, system logs, such as kernel activities are logged in syslog file.

Some of the most common log files in that directory is :

• In directory apt there is a file history.log which saves all the package installation and removal information even the initial system build as Live CD. You can open this file to see this very interesting file.

• In directory dist-upgrade there is a file apt.log which logs the information during distribution upgrades

• In directory installer the log files which are created during installation can be found.

• There is an apport.log file which saves information about crashes in your system and reporting them.

• The file auth.log includes information about the authentication activities such as when you authenticate as root user via sudo.

• The file dpkg.log saves the low level details of package installation and removal related with dpkg. You might be aware that the apt system depends on dpkg for package installation and removal.

• boot.log includes information of each booting.

• kern.log saves kernel information such as warnings, errors etc.

• alternatives.log includes the history of all the alternatives set by various packages and their removal via update-alternatives command.

• Another important log file is Xorg.log which include information about the graphics driver, its failures, warnings etc.

Some other types of Log files may be there depending on your installed packages. For example, My system also includes a log files epoptes.log which will only be there if you install epoptes package.

Changes after systemd

With the advent of systemd, logging is mostly handled by journalctl utility and store the logs in binary format in /var/lib/systemd/catalog/database file. This file enumerates all logs including kernel, boot and application logs and provides required logs via journalctl utility.

Here is a good article on journalctl on how you can use it to fetch required log info.

https://www.digitalocean.com/community/tutorials/how-to-use-journalctl-to-view-and-manipulate-systemd-logs#setting-the-system-time

By looking at this line in the following line in the log, it appears that Apparmor is denying access.

Jan  2 12:09:36 praveshp-lt kernel: [ 7060.098580] type=1400 audit(1357108776.036:33):
     apparmor="DENIED" operation="mknod" parent=6702 profile="/usr/sbin/mysqld" 
     name="/run/mysqld/mysqld1.sock" pid=7039 comm="mysqld" requested_mask="c"
     denied_mask="c" fsuid=116 ouid=116

To allow this, add a file /etc/apparmor.d/local/usr.sbin.mysqld with the entry below, and restart MySQL.

/var/run/mysqld/mysqld1.sock w,

Thanks to Rinzwind for pointing this out.