Process Priorities

Server Process Priorities

Especially for Linux (Ubuntu)


PS Usage and Examples

ps creates a list of all running processes.

ps -al

Look under the NI list for process niceness (priority). Priorities run from -20 to 20 (highest priority to lowest).

 

Nice Usage and Examples

Nice runs a command (creates a process) with a set priority.

sudo nice -priority command

Setting a -20 priority is –20, while a 20 priority is -20

Because it may not be possible to separate processes into users, nice can be used with cron to call services with specific priorities. For example, a virus scanner should not take priority over apache on a webserver.

sudo crontab -e

Prefix cron commands with nice -priority. For example, Sophos AV:

00 11,16 * * * nice -20 savscan -all -pua -suspicious --examine-x-bit -archive /

 

Other Commands

renice – alter priority of running processes

ionice – set or retrieve the I/O priority for a given pid or execute a new task with a given I/O priority.

iostat – report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.

ulimit – provide control over the resources available to processes started by the shell on systems that allow such control.

chrt – set or retrieve real-time scheduling parameters for a given pid or execute a new task under given scheduling parameters.

taskset – set or retrieve task CPU affinity for a given pid or execute a new task under a given affinity mask.

From AskApache.

 

Default Niceness for Specific Users

For servers, it may be a good idea to separate processes (mysql, www-data, etc) for both security and process niceness. For example, the web server should never be run as root.

To set niceness for users permanently, run this command and input the desired values:

sudo nano /etc/security/limits.conf

Syntax:  [username] [hard|soft] priority [nice value]

backupuser hard priority 1

References: 1, 2

 

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