How to get the start time of a long-running Linux process?

Is it possible to get the start time of an old running process? It seems that ps will report the date (not the time) if it wasn't started today, and only the year if it wasn't started this year. Is the precision lost forever for old processes?

8 Answers

You can specify a formatter and use lstart, like this command:

ps -eo pid,lstart,cmd 

The above command will output all processes, with formatters to get PID, command run, and date+time started.

Example (from Debian/Jessie command line)

$ ps -eo pid,lstart,cmd PID CMD STARTED 1 Tue Jun 7 01:29:38 2016 /sbin/init 2 Tue Jun 7 01:29:38 2016 [kthreadd] 3 Tue Jun 7 01:29:38 2016 [ksoftirqd/0] 5 Tue Jun 7 01:29:38 2016 [kworker/0:0H] 7 Tue Jun 7 01:29:38 2016 [rcu_sched] 8 Tue Jun 7 01:29:38 2016 [rcu_bh] 9 Tue Jun 7 01:29:38 2016 [migration/0] 10 Tue Jun 7 01:29:38 2016 [kdevtmpfs] 11 Tue Jun 7 01:29:38 2016 [netns] 277 Tue Jun 7 01:29:38 2016 [writeback] 279 Tue Jun 7 01:29:38 2016 [crypto] ... 

You can read ps's manpage or check Opengroup's page for the other formatters.

The ps command (at least the procps version used by many Linux distributions) has a number of format fields that relate to the process start time, including lstart which always gives the full date and time the process started:

# ps -p 1 -wo pid,lstart,cmd PID STARTED CMD 1 Mon Dec 23 00:31:43 2013 /sbin/init # ps -p 1 -p $$ -wo user,pid,%cpu,%mem,vsz,rss,tty,stat,lstart,cmd USER PID %CPU %MEM VSZ RSS TT STAT STARTED CMD root 1 0.0 0.1 2800 1152 ? Ss Mon Dec 23 00:31:44 2013 /sbin/init root 5151 0.3 0.1 4732 1980 pts/2 S Sat Mar 8 16:50:47 2014 bash 

For a discussion of how the information is published in the /proc filesystem, see

(In my experience under Linux, the time stamp on the /proc/ directories seem to be related to a moment when the virtual directory was recently accessed rather than the start time of the processes:

# date; ls -ld /proc/1 /proc/$$ Sat Mar 8 17:14:21 EST 2014 dr-xr-xr-x 7 root root 0 2014-03-08 16:50 /proc/1 dr-xr-xr-x 7 root root 0 2014-03-08 16:51 /proc/5151 

Note that in this case I ran a "ps -p 1" command at about 16:50, then spawned a new bash shell, then ran the "ps -p 1 -p $$" command within that shell shortly afterward....)

As a follow-up to Adam Matan's answer, the /proc/<pid> directory's time stamp as such is not necessarily directly useful, but you can use

awk -v RS=')' 'END{print $20}' /proc/12345/stat 

to get the start time in clock ticks since system boot.¹

This is a slightly tricky unit to use; see also convert jiffies to seconds for details.

awk -v ticks="$(getconf CLK_TCK)" 'NR==1 { now=$1; next } END { printf "%9.0f\n", now - ($20/ticks) }' /proc/uptime RS=')' /proc/12345/stat 

This should give you seconds, which you can pass to strftime() to get a (human-readable, or otherwise) timestamp.

awk -v ticks="$(getconf CLK_TCK)" 'NR==1 { now=$1; next } END { print strftime("%c", systime() - (now-($20/ticks))) }' /proc/uptime RS=')' /proc/12345/stat 

Updated with some fixes from Stephane Chazelas in the comments; thanks as always!

If you only have Mawk, maybe try

awk -v ticks="$(getconf CLK_TCK)" -v epoch="$(date +%s)" ' NR==1 { now=$1; next } END { printf "%9.0f\n", epoch - (now-($20/ticks)) }' /proc/uptime RS=')' /proc/12345/stat | xargs -i date -d @{} 

¹ man proc; search for starttime.

ls -ltrh /proc | grep YOUR-PID-HERE 

For example, my Google Chrome's PID is 11583:

ls -l /proc | grep 11583 dr-xr-xr-x 7 adam adam 0 2011-04-20 16:34 11583 

 ps -eo pid,cmd,lstart | grep YOUR-PID-HERE 

$ ps -p 182454 -o lstart= Mon Oct 18 17:26:44 2021 

But can I get the answer in epoch seconds?

 ps -eo pid,etime,cmd|sort -n -k2 

use the command ls -ld /proc/process_id where process_id can be find using top command