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Knowing how long a process has been running can be useful. Unfortunately, the standard date fields in the
ps command use a “scrolling date” display. In other words, it displays uptime differently based on a process's age. Here's an example:
me@mybox:~$ ps aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND nobody 22571 0.0 0.0 2128 244 ? SN 08:22 0:00 /usr/sbin/tinyproxy nobody 22572 0.0 0.0 2128 244 ? SN 08:22 0:00 /usr/sbin/tinyproxy root 21075 0.0 0.0 0 0 ? S< Apr26 0:00 [kstriped] root 21082 0.0 0.0 0 0 ? S< Apr26 0:00 [ksnapd] root 17275 0.0 1.5 178952 74028 ? Ss 2008 0:18 /usr/sbin/httpd ....
Notice that the first two processes say
08:22 in the
START column. Those processes were started today. I only know that because I read the
man page. The next two processes say
Apr26 which is clear enough, but I've lost the timestamp. And the last process only says 2008. No date, no time.
This is not a very script-friendly way to display the date. If I wanted to use the start time in a script, I would have to codify the things I mentioned above. In other words, I would need to parse the
START column and determine all the parts of the date based on my understanding of
ps's behavior. Definitely not a good idea since
ps could change.
So how do I find the complete and accurate start time? There are a couple ways.
I stole this example from the
ps man page, with adjustments. The man page says:
To see every process with a user-defined format: ps -eo pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:14,comm
The important thing is the
-o command line option which allows me to customize the columns I want to see in the output. Further down the
ps man page, I found the
STANDARD FORMAT SPECIFIERS section, which revealed these tidbits:
etime elapsed time since the process was started, in the form [[dd-]hh:]mm:ss. pid process ID number of the process. args command with all its arguments as a string
So now I can run a simple command:
me@mybox:~$ ps -eo pid,etime,args 22571 01:06:40 /usr/sbin/tinyproxy 22572 01:06:40 /usr/sbin/tinyproxy 21075 2-15:05:35 [kstriped] 21082 2-15:05:35 [ksnapd] 17275 373-00:07:49 /usr/sbin/httpd
Notice the time output now. The first two processes have hours, minutes, and seconds. The next three processes reveal the number of days they've been alive (with a dash between the day and hour). This is something I can work with. But how do we know the start date of the process? Fortunately, the
date command helps me there:
me@mybox:~$ date -d '-373 days' Mon Apr 21 09:42:34 EDT 2008
And most importantly, I can capture the date object in a shell script and use it if I need to.