Seeing what background process is up to

Question

I currently have a background process on my unix server that's running hours longer than it should be.

I can't remember the command to allow me to see the output of a background process. I'll remember to bookmark this answer!

Answer 1

What also might be useful if you're uncertain whether it's doing anything at all, is use 'strace'.

If your app is the 'dhcpd' service, run ps ax | grep [d]hcpd

$ ps axufw | grep [d]hcpd
dhcpd    21645  0.0  0.1  19156  4956 ?        Ss   Oct02   0:00 /usr/sbin/dhcpd -f -q -4 -pf /run/dhcp-server/dhcpd.pid -cf /etc/ltsp/dhcpd.conf

Your PID is 21645, so you'd run sudo strace -p 21645. Or drop the 'sudo' if you're root already.

It will get the system calls from your application in real time and tell you precisely what your program is doing.

Note: Wrap a letter of the grep command in a bracket to strain out the grep command itself.

Answer 2

As a follow up to Mariano Montañez Ureta.

If you can see the task in the jobs window, all you should be able to see something like this:

$ jobs
[1]+  Running                 tail -f .ssh/known_hosts &

If you then use the fg command coupled with the job number you can bring that to the foreground, i.e. fg %1 would bring my tail command to the foreground. You can also use the fg command with a PID.

Answer 3

use fg wich means foreground :)

Answer 4

tail -f whatever-file-the-process-is-writing-to.txt