I have to copy files on a machine. And the data is immensely large. Now servers need to serve normally, and there are usually a particular range of busy hours on those. So is there a way to run such commands in a way that if server hits busy hours, it pauses process, and when it gets out of that range, it resumes it?
Intended-Result
cp src dst
if time between 9:00-14:00 pause process
After 14:00 resume cp command.
You can pause execution of a process by sending it a SIGSTOP signal and then later resume it by sending it a SIGCONT.
Assuming your workload is a single process (doesn't fork helpers running in background), you can use something like this:
# start copy in background, store pid
cp src dst &
echo "$!" >/var/run/bigcopy.pid
Then when busy time starts, send it a SIGSTOP:
# pause execution of bigcopy
kill -STOP "$(cat /var/run/bigcopy.pid)"
Later on, when the server is idle again, resume it.
# resume execution of bigcopy
kill -CONT "$(cat /var/run/bigcopy.pid)"
You will need to schedule this for specific times when you want it executed, you can use tools such as cron or systemd timers (or a variety of other similar tools) to get this scheduled. Instead of scheduling based on a time interval, you might choose to monitor the server (perhaps looking at load average, CPU usage or activity from server logs) to make a decision of when to pause/resume the copy.
You also need to manage the PID file (if you use one), make sure your copy is actually still running before pausing it, probably you'll want to clean up by removing the PID file once the copy is finished, etc.
In other words, you need more around this to make a reliable, but the base idea of using these SIGSTOP and SIGCONT signals to pause/resume execution of a process seems to be what you're looking for.
ps -eo pid,command could be used to ensure the pid is running and that the command line of the process matches what you expect: just store command="full command", invoke as $command, then make pid file match what ps -eo you'd expect when you want to SIGCONT: cmd="stuff here" ; $cmd & echo "$? $cmd" > psfile ; then later if ps -eo pid,command | grep -q $(cat psfile); then echo "it's alive!" fi
Instead of suspending the process, you could also give it lower priority:
renice 19 "$pid"
will give it the lowest priority (highest niceness), so that process will yield the CPU to other processes that need it most of the time.
On Linux, the same can be done with I/O with ionice:
ionice -c idle -p "$pid"
Will put the process in the "idle" class, so that it will only get disk time when no other program has asked for disk I/O for a defined grace period.
Yes, you need to acquire the process id of the process to pause (via the ps command), then do:
$> kill -SIGSTOP <pid>
The process will then show up with Status "T" (in ps).
To continue, do a:
$> kill -CONT <pid>
Use rsync, forget about cp, for this scenario. there are params to limit bandwith, or can be killed/stoped and started later, in a way it will continue, where it left google rsync example/s
If you are going to do it by interrupting the running process, I suggest playing with the Screen program. I haven't used Linux in a while, but IIRC just pausing the command and resuming it later leaves you pretty vulnerable, if you accidentally get logged off you won't be able to resume your session.
With screen I believe you can interrupt the session then detach it and log out. Later you can go back in and reattach to that session. You'd have to play with it a bit but it made sessions much more robust.
You can also log out and go home then log in remotely, reattach to the system y you started in the office and resume it for the evening, then pick it up again the next day at work.
If your shell supports it (almost all do), you can press ^Z (Ctrl+Z) to easily send a SIGTSTP signal to the foreground task, then continue it with fg (on foreground) or bg (on background).
If you do this on multiple tasks and want to return to them later, you can use jobs command, then return with fg/bg %#, where # is the number given in brackets on jobs.
Keep in mind that SIGTSTP is a bit different than SIGSTOP (which is used on all other answers), most importantly due to the fact that it can be ignored (but I didn't see a program ignore it other than sl). More details can be found on this answer on StackOverflow.
cp -alto make a hardlink farm? Or use a filesystem that supports block-level reflinks with copy-on-write, usingcp -a --reflink=auto? BTRFS and ZFS support that for copies within the same physical device.srcchange between 9:00 and 14:00? If so, simply pausing and resuming thecpprocess may result in corrupted files. It may be better to runrsyncin combination with thetimeoutcommand.