That's what might be useful even for web-developers, not just sysadmins and geeky geeks.
Often there is a need to check what's some process doing right now. `top` is of course showing us 100% of CPU consumption but you need to have some sort of progress to decide if you can wait or you'll just kill the task and do it in a different way.
Let's take `grep` as an example of some task that may take hours on a big set of files:
user@host [/tmp/files] $ grep -e "$PATTERN" *.dat
So to use magic you don't need patch grep or to have knowledge of how to debug Linux kernel. I use `/proc` for this task:
- Find PID of the grep process, like this "ps axuww | grep grep" :)
- Exec "ls -al /proc/$PID/fd/"
- You'll get directory list as an output. One of these file descriptors the a process is grep's current file it's processing right now.
lrwx------ 1 user 64 2009-07-05 04:12 0 -> /dev/pts/2
lrwx------ 1 user 64 2009-07-05 04:12 1 -> /dev/pts/2
lrwx------ 1 user 64 2009-07-05 04:12 2 -> /dev/pts/2
lr-x------ 1 user 64 2009-07-05 04:12 3 -> /tmp/files/2009-07-01_4534545435.dat
Voila!
For progress calculation you can use "ls *.dat > list.txt" and then find which line you on right now.
