How to find uptime of a linux process

Solution 1:

As "uptime" has several meanings, here is a useful command.

ps -eo pid,comm,lstart,etime,time,args

This command lists all processes with several different time-related columns. It has the following columns:

PID COMMAND                          STARTED     ELAPSED     TIME COMMAND

PID = Process ID
first COMMAND = only the command name without options and without arguments
STARTED = the absolute time the process was started
ELAPSED = elapsed time since the process was started (wall clock time), format [[dd-]hh:]mm:ss TIME = cumulative CPU time, "[dd-]hh:mm:ss" format
second COMMAND = again the command, this time with all its provided options and arguments

Solution 2:

If you have a limited version of ps such as is found in busybox, you can get the process start time by looking at the timestamp of /proc/<PID>. For example, if the pid you want to look at is 55...

# ls -al /proc | grep 55
dr-xr-xr-x    7 root     root             0 May 21 05:53 55

... and then compare it with the current date...

# date
Thu May 22 03:00:47 EDT 2014

Solution 3:

I think you can just run:

$ stat /proc/1234

1234 being the process id.

example with two processes started at the same hour minute seconds but not the same milliseconds:

$ stat /proc/9355
...
Access: 2017-11-13 17:46:39.778791165 +0100
Modify: 2017-11-13 17:46:39.778791165 +0100
Change: 2017-11-13 17:46:39.778791165 +0100
$ stat /proc/9209
...
Access: 2017-11-13 17:46:39.621790420 +0100
Modify: 2017-11-13 17:46:39.621790420 +0100
Change: 2017-11-13 17:46:39.621790420 +0100