I have 30 instances of a process running on a server and want to log open files for each process for analysis.
I ran the following command:
* ps auw
The lsof -p option takes a comma-separated list of PIDs. The way you're using xargs will pass the pids as separate arguments leading some to be interpreted as filenames.
Try lsof -p $(your grep | tr '\012' ,) That's going to have a trailing comma, I'm not sure if lsof will care but you could sed it off if necessary.
You can use xargs -L1 lsof -p to run lsof once per pid.
Even better: use lsof -c to list all open files from commands matching a specific pattern:
lsof -c bas # list all processes with commands starting with 'bas'
lsof -c '/ash$/x' # list all commands ending with 'ash' (regexp syntax)