Today we had the problem, that a recursive grep was hanging without any output. First approach was to look at what grep was doing:
ps -ef | grep grep strace -p GREP_PID
Grep tried to read a file supervise uses:
# strace -p 4522 Process 4522 attached - interrupt to quit open("clamd/supervise/ok", O_RDONLY) = ? ERESTARTSYS (To be restarted)
After a quick Google search StackOverflow brought the solution - add -D skip to the grep command to skip sockets and FIFO files. I’ve added the following line to my _.bash[rc|profile]:
alias grep='grep -D skip'