SYS: Identify CPU/memory intensive processes, adjust process priority with renice, and kill processes.

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Note: This is an RHCSA 7 exam objective.

System Activities

To get an instantaneous image of a server activity (use ‘virt-top‘ on a KVM hypervisor), type:

# top

To get details about processes, type:

# ps -edf

Process Priority

To start a process (here with a low priority, type:

# nice -n 10 ./

To change the priority (here +5) of an already running process, get its PID (Process ID) through top or ps (here 789) and type:

# renice +5 789


# renice +5 `pgrep`

Process Deletion

To kill the process, get its PID through top or ps (here 789) and type:

# kill -9 789


# pkill

System Reporting

To display details about IO activities, type:

# iostat

To show network card activities, type:

# netstat -i

To display socket activities, type:

# netstat -a

To get details about virtual memory activities (memory, swap, run queue, cpu usage, etc) every 5 second, type:

# vmstat 5

To get a full report of a server activity, type:

# sar -A

Additional Resources

You can also watch a video by Sander van Vugt about Understanding Linux Memory Usage (4min/2016).

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Just a comment about `kill -9` This is not the default behavior and rarely used on for well written programs. `kill` sends SIGTERM as default to a process so the process needs time for a clean up of open files, FD’s etc.


I guess PackageKit isn’t a well written program, since I have to put up a fight with it first via several kill -9 on it before being able to use yum install to install stuff on my virtual CentOS installation.


Long time Solaris / Linux newbie. A note on sar that is probably apparent to most but I had to do a look up on it: it is a part of the sysstat tool set that did not get installed on my minimum distro.
yum install sysstat
Great site, using it for RHCSA at the moment and feeling pretty well prepared after a week of intense studying!

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