What does EAGAIN mean?

Question

As in the title what does EAGAIN mean?

Answer 1

What it means is less important. What it implies:

• your system call failed
• nothing happened (system calls are atomic, and this one just did not happen)
• you could try it again (it could fail again, possibly with a different result)
• or you could choose otherwise.

The whole thing about EAGAIN is that your process is not blocked inside the system call; it has the right to choose: either retry or do something useful.