Get the age of a process?

Question

How can I see the age (in seconds) of a process in Linux? I want to do it in a script. ps has various start/lstart/start_time options, which show a textual format for the date & time the process started. How can I get an integer representing the number of seconds elapsed since that start time?

Answer 1

suppose you want to know how many seconds have passed since the start of process 12345, then you execute

ps -p 12345 -o etimes=

For example:

$ date; ps -fp 2184; ps -fp 2184 -o etimes=
ma apr 20 20:00:38 CEST 2020
UID        PID  PPID  C STIME TTY          TIME CMD
root      2184     1  0 12:09 ?        00:00:00 /usr/sbin/apache2 -k start
28286

Apache was started 28286 seconds before I executed above commands.

PS. There is an old tool on unix systems, called "man".