How to check how long a process has been running?
On Linux with the ps from procps(-ng) (and most other systems since this is specified by POSIX):
Where $$ is the PID of the process you want to check. This will return the elapsed time in the format [[dd-]hh:]mm:ss .
Using -o etime tells ps that you just want the elapsed time field, and the = at the end of that suppresses the header (without, you get a line which says ELAPSED and then the time on the next line; with, you get just one line with the time).
Or, with newer versions of the procps-ng tool suite (3.3.0 or above) on Linux or on FreeBSD 9.0 or above (and possibly others), use:
(with an added s ) to get time formatted just as seconds, which is more useful in scripts.
On Linux, the ps program gets this from /proc/$$/stat , where one of the fields (see man proc ) is process start time. This is, unfortunately, specified to be the time in jiffies (an arbitrary time counter used in the Linux kernel) since the system boot. So you have to determine the time at which the system booted (from /proc/stat ), the number of jiffies per second on this system, and then do the math to get the elapsed time in a useful format.
It turns out to be ridiculously complicated to find the value of HZ (that is, jiffies per second). From comments in sysinfo.c in the procps package, one can A) include the kernel header file and recompile if a different kernel is used, B) use the posix sysconf() function, which, sadly, uses a hard-coded value compiled into the C library, or C) ask the kernel, but there’s no official interface to doing that. So, the ps code includes a series of kludges by which it determines the correct value. Wow.
So it’s convenient that ps does that all for you. 🙂
start time of a process on linux
How to find a process start time on ubuntu linux machine using c language. In linux there is /proc/[pid]/stat file which give information starttime %lu /*The time in jiffies the process started after system boot*/
and file /proc/stat that gives
btime %lu /*measurement of system boot time since Epoch in seconds*/ For adding both these values how can I convert former value into seconds because it is in jiffies unit.
1 Answer 1
Jiffies per second is configurable when one compiles the Linux kernel.
The following program uses the number of jiffies per second on the kernel you’re running. It takes an optional command line parameter, which is the process number. The default is the process number of the running program itself. Each second, it outputs the start time of the specified process, both as local time and UTC. The only reason for the repeat loop is to demonstrate that the value doesn’t change.
#include #include #include #include #include #include #include #include int find_nth_space(char *search_buffer, int space_ordinality ) < int jndex; int space_count; space_count=0; for(jndex=0; search_buffer[jndex]; jndex++ ) < if(search_buffer[jndex]==' ') < space_count++; if(space_count>=space_ordinality) < return jndex; >> > fprintf(stderr,"looking for too many spaces\n"); exit(1); > /* find_nth_space() */ int main(int argc, char **argv ) < int field_begin; int stat_fd; char proc_buf[80]; char stat_buf[2048]; long jiffies_per_second; long long boot_time_since_epoch; long long process_start_time_since_boot; time_t process_start_time_since_epoch; ssize_t read_result; struct tm gm_buf; struct tm local_buf; jiffies_per_second=sysconf(_SC_CLK_TCK); if(argc<2) < strcpy(proc_buf,"/proc/self/stat"); >else < sprintf(proc_buf,"/proc/%ld/stat",strtol(argv[1],NULL,0)); >for(;;) < stat_fd=open(proc_buf,O_RDONLY); if(stat_fd<0) < fprintf(stderr,"open() fail\n"); exit(1); >read_result=read(stat_fd,stat_buf,sizeof(stat_buf)); if(read_result <0) < fprintf(stderr,"read() fail\n"); exit(1); >if(read_result>=sizeof(stat_buf)) < fprintf(stderr,"stat_buf is too small\n"); exit(1); >field_begin=find_nth_space(stat_buf,21)+1; stat_buf[find_nth_space(stat_buf,22)]=0; sscanf(stat_buf+field_begin,"%llu",&process_start_time_since_boot); close(stat_fd); stat_fd=open("/proc/stat",O_RDONLY); if(stat_fd <0) < fprintf(stderr,"open() fail\n"); exit(1); >read_result=read(stat_fd,stat_buf,sizeof(stat_buf)); if(read_result <0) < fprintf(stderr,"read() fail\n"); exit(1); >if(read_result>=sizeof(stat_buf)) < fprintf(stderr,"stat_buf is too small\n"); exit(1); >close(stat_fd); field_begin=strstr(stat_buf,"btime ")-stat_buf+6; sscanf(stat_buf+field_begin,"%llu",&boot_time_since_epoch); process_start_time_since_epoch = boot_time_since_epoch+process_start_time_since_boot/jiffies_per_second; localtime_r(&process_start_time_since_epoch,&local_buf); gmtime_r (&process_start_time_since_epoch,&gm_buf ); printf("local time: %02d:%02d:%02d\n", local_buf.tm_hour, local_buf.tm_min, local_buf.tm_sec ); printf("UTC: %02d:%02d:%02d\n", gm_buf.tm_hour, gm_buf.tm_min, gm_buf.tm_sec ); sleep(1); > return 0; > /* main() */ 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?
Is there anything wrong with using ps -p
@ajwood It would be better to use ps -p
Is there anything wrong with using ps -p -o lstart ? Maybe the fact there’s no lstart neither in 2004 Edition nor in 2013 Edition of POSIX 1003.1 standard?
@PiotrDobrogost, that would be a problem if the question asked about POSIX, but it’s asking about Linux.
Mods — techraf, Makyen, David Rawson, Tsyvarev, Paul Roub — why don’t you move it to a more appropriate site such as StackExchange or Superuser instead of closing the question? This is a good and useful question
8 Answers 8
You can specify a formatter and use lstart , like this command:
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.
Be aware that lstart time can change, the stat methods below are safer — unix.stackexchange.com/questions/274610/….
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 $$ -wo user,pid,%cpu,%mem,vsz,rss,tty,stat,lstart,cmd USER PID %CPU %MEM VSZ RSS TT STAT STARTED CMD root 1 0.0 0.1 2800 1152 ? Ss Mon Dec 23 00:31:44 2013 /sbin/init root 5151 0.3 0.1 4732 1980 pts/2 S Sat Mar 8 16:50:47 2014 bash (In my experience under Linux, the time stamp on the /proc/ directories seem to be related to a moment when the virtual directory was recently accessed rather than the start time of the processes:
# date; ls -ld /proc/1 /proc/$$ 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. )
How to find uptime of a linux process
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
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/ . 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 can generate the etimes= with proc entries like etime=$(date -d «$(stat -c %y /proc/$
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 yes, too old and yet too hard stuff. I tried with the above proposed «stat» method but what if I had «touch»-ed the PID proc dir yesterday? This means my year-old process is shown with yesterday’s time stamp. Nah, not what I need 🙁
In the newer ones, it’s simple:
ps -o etimes -p ELAPSED 339521 as simple as that. Time is present in seconds. Do whatever you need it for. With some older boxes, situation is harder, since there’s no etimes. One could rely on:
ps -o etime -p ELAPSED 76-03:26:15 which look a «a bit» weird since it’s in dd-hh:mm:ss format. Not suitable for further calculation. I would have preferred it in seconds, hence I used this one:
ps -o etime -p --no-headers | awk -F '(:)|(-)' 'BEGIN;=1;i--) s=s+a[i]*$i>END' 339544 do not parse the output of etime because busybox 1.29.3 changed the format. use the stat + /proc method instead
Such a simple thing is not properly answered after 5 years?
I don’t think you can accurately get milliseconds. eg. if you see man procfs and see /proc/$$/stat which has field 22 as startime, which is in «clock ticks», you would have something more precise, but clock ticks aren’t going at a perfectly constant rate (relative to ‘wall clock time’) and will be off. sleeping and certain things (ntpd I guess) offset it. For example on a machine running ntpd, with 8 days uptime and has never slept, dmesg -T has the same problem (I think. ), and you can see it here:
# date; echo h > /proc/sysrq-trigger; dmesg -T | tail -n1 ; date Fri Mar 3 10:26:17 CET 2017 [Fri Mar 3 10:26:16 2017] sysrq: SysRq : HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(V) show-blocked-tasks(w) Fri Mar 3 10:26:17 CET 2017 # example pid here is just your shell pid=$$ # current unix time (seconds since epoch [1970-01-01 00:00:00 UTC]) now=$(date +%s) # process start unix time (also seconds since epoch) # I'm fairly sure this is the right way to get the start time in a machine readable way (unlike ps). but could be wrong start=$(stat -c %Y /proc/"$pid") # simple subtraction (both are in UTC, so it works) age=$((now-start)) printf "that process has run for %s seconds\n" "$age"