How to check how long a process has been running?

ps takes a -o option to specify the output format, and one of the available columns is etime. According to the man page:

etime – elapsed time since the process was started, in the form [[dd-]hh:]mm:ss.

Thus you can run this to get the PID and elapsed time of every process:

$ ps -eo pid,etime

If you want the elapsed time of a particular PID (e.g. 12345), you can do something like:

$ ps -eo pid,etime | awk '/^12345/ {print $2}'

(Edit: Turns out there’s a shorter syntax for the above command; see mattdm’s answer)

Portable:

% ps -o stime,time $$
STIME     TIME
Jan30 00:00:06

i.e. that shell was started on January 30 and totaled about 6 seconds of CPU time.

There may be more precise or more parseable but less portable ways to get this information. Check the documentation of your ps command or your proc filesystem.

Under Linux, this information lives in /proc/$pid/stat.

awk '{print "CPU time: " $14+$15; print "start time: " $22}' /proc/$$/stat

The CPU time is in jiffies; I don’t know offhand how to find the jiffy value from the shell. The start time is relative to the boot time (found in /proc/uptime).

If you can run time and then execute a command you will get exactly what you are looking for. You cannot do this against an already-running command.

[0] % time sleep 20

sleep 20 0.00s user 0.00s system 0% cpu 20.014 total

If you dont know the PID of the process, just the name:

ps -eo pid,comm,cmd,start,etime | grep -i <name of the process>

If you know the PID:

ps -o pid,comm,cmd,start,etime -p <PID>

Unsure why this has not yet been suggested: on Linux you can stat() the /proc/[nnn] directory for your PID.

This behavior is explicitly designed to return the process start time, which it can do at high resolution, and which the kernel can do accurately without the jiffies hacks since the kernel can (obviously) simply check the relevant information. The access, data-modification and status change fields all return the process start time.

Best of all, you can use stat(1) at the shell, or the appropriate binding to stat(2) from $favorite_programming_language, so you may not even need to launch an external process.

NOTE that this does not work with /usr/compat/linux/proc on FreeBSD; the access/modification/status-change times returned are the current time, and the birth time is the UNIX epoch. Quite stupid the support isn’t there if you ask me.

you can get the start time of the process by looking at the stat of the stat file produced by proc, format it using date and subtract it from the current time:

echo $(( $(date +%s) - $(date -d "$(stat /proc/13494/stat | grep Modify | sed 's/Modify: //')" +%s) ))

where 13494 is your process’ pid

$ ps -eo lstart get start time

$ ps -eo etime get duration/elapsed time

$ ps -eo pid,lstart,etime | grep 61819
  PID                   STARTED     ELAPSED
  61819 Mon Sep 17 03:01:35 2018    07:52:15

61819 is the process id.

Time elapsed in seconds: expr $(date +"%s") - $(stat -c%X /proc/<PID HERE>)

A handy function based on “ps -o etime=” and “bc” to help with the maths and the
zero left padded numbers.

Give it the pid and get the running minutes back.

function running_time (){
  # correct up to 100 days! #08:28:40 #53:32 #15-01:23:00
  p=$1 ; i=$(ps -o etime= $p) ; i=$(echo $i) ;

  len=${#i}
  [[ $len == 5  ]] && i="00-00:$i" ; [[ $len == 8  ]] && i="00-$i"
  [[ $len == 10 ]] && i="0$i"

  mins=$(echo ${i:0:2}*24*60+${i:3:2}*60+${i:6:2}|bc)
  echo $mins
}

I wanted it in seconds and I came up with (pure bash):

runtime=$(ps -o etime= -p <pid>)
runtime=$(date -d "1970-01-01 $((10#${runtime: -8: 2})):$((10#${runtime: -5: 2})):$((10#${runtime: -2: 2}))Z + $((10#$(echo "$runtime" | grep -oP "[0-9]+(?=-)"))) days" +%s)

The problem with etime is, that some values are optional.

Because of that I used $((10#string)) to convert empty strings to 0 and by that the final date string will be something like this for a short running process:

date -d "1970-01-01 0:0:7Z + 0 days" +%s

and like this for a long runnning processs:

date -d "1970-01-01 12:45:11 + 253 days" +%s

Using date to convert to seconds was inspired by this answer.

On FreeBSD, you have to use the command keyword instead of comm:

root@freebsd:~ # ps x -o etime,command | grep -e sshd -e syslogd -e cron
 53-00:42:12 /usr/sbin/syslogd -s
 57-01:26:52 /usr/sbin/cron -s
    10:02:09 sshd: /usr/sbin/sshd [listener] 0 of 10-100 startups (sshd)
       20:29 sshd: charlie [priv] (sshd)
       00:00 grep -e sshd -e syslogd -e cron

The first column now contains the information on how long the process is running. It is in the following format:

[days-][hours:]minutes:seconds

You may want to use etimes instead of etime to get that information in seconds.