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pidfd_open.2: Note the waitid() use case for PID file descriptors 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2019-10-12 22:40:09 +02:00
parent d069725512
commit 9e1b1cd286
1 changed files with 7 additions and 1 deletions
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8
man2/pidfd_open.2
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@ -169,6 +169,10 @@ nothing can be read from the file descriptor
.RB ( read (2)
on the file descriptor fails with the error
.BR EINVAL ).
.IP *
If the PID file descriptor refers to a child of the calling process,
then it can be waited on using
.BR waitid (2).
.PP
The
.BR pidfd_open ()
@ -182,7 +186,8 @@ However, the latter technique is possible only if the
file system is mounted;
furthermore, the file descriptor obtained in this way is
.I not
pollable.
pollable and can't be waited on with
.BR waitid (2).
.SH EXAMPLE
The program below opens a PID file descriptor for the
process whose PID is specified as its command-line argument.
@ -251,4 +256,5 @@ main(int argc, char *argv[])
.BR pidfd_send_signal (2),
.BR poll (2),
.BR select (2),
.BR waitid (2),
.BR epoll (7)