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Editorial Team
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Asked: 2026-06-14T05:55:05+00:00

Some system calls can be restarted transparently by the Kernel if the SA_RESTART flag

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Some system calls can be restarted transparently by the Kernel if the SA_RESTART flag is used when installing the signal handler, according to man signal(7):

If a blocked call to one of the following interfaces is interrupted
by a signal handler, then the call will be automatically restarted
after the signal
handler returns if the SA_RESTART flag was used; otherwise the call will fail with the error EINTR:

Then it mentions some system calls that can (and can not) be restarted, but does not mention close() in either places, how would I know if close(), or any other function, is restartable or not ? does POSIX specify it or is it a Linux-specific behaviour ? where can I find more info ?

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1 Answer

  1. Editorial Team

    As per POSIX.1-2008, the SA_RESTART flag applies to all interruptible functions (all function which are documented to fail with EINTR):

    SA_RESTART

    This flag affects the behavior of interruptible functions; that is, those specified to fail with errno set to [EINTR]. If set, and a function specified as interruptible is interrupted by this signal, the function shall restart and shall not fail with [EINTR] unless otherwise specified. If an interruptible function which uses a timeout is restarted, the duration of the timeout following the restart is set to an unspecified value that does not exceed the original timeout value. If the flag is not set, interruptible functions interrupted by this signal shall fail with errno set to [EINTR].

    That is, the list of functions which are not restarted is Linux-specific (and probably counts as a bug).

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