InformationThe /var/log directory is used by system services to store log data.
The reasoning for mounting /var/log on a separate partition is as follow.
Protection from resource exhaustion
The default installation only creates a single / partition. Since the /var/log directory contain the log files that can grow quite large, there is a risk of resource exhaustion. It will essentially have the whole disk available to fill up and impact the system as a whole.
Fine grained control over the mount
Configuring /var/log as its own file system allows an administrator to set additional mount options such as noexec/nosuid/nodev. These options limits an attackers ability to create exploits on the system. Other options allow for specific behavior. See man mount for exact details regarding filesystem-independent and filesystem-specific options.
Protection of log data
As /var/log contains log files, care should be taken to ensure the security and integrity of the data and mount point.
Resizing filesystems is a common activity in cloud-hosted servers. Separate filesystem partitions may prevent successful resizing, or may require the installation of additional tools solely for the purpose of resizing operations. The use of these additional tools may introduce their own security considerations.
SolutionFor new installations, during installation create a custom partition setup and specify a separate partition for /var/log .
For systems that were previously installed, create a new partition and configure /etc/fstab as appropriate.