What does EAGAIN mean? What does EAGAIN mean? unix unix

What does EAGAIN mean?


c sockets unix posix

EAGAIN is often raised when performing non-blocking I/O. It means "there is no data available right now, try again later".

It might (or might not) be the same as EWOULDBLOCK, which means "your thread would have to block in order to do that".

c sockets unix posix

Using man 2 intro | less -Ip EAGAIN:

     35 EAGAIN Resource temporarily unavailable.  This is a temporary condi-         tion and later calls to the same routine may complete normally.

c sockets unix posix

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.

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