ERESTARTSYS

ERESTARTSYS is a Linux kernel error code used to indicate that a system call was interrupted by a signal and should be restarted if the signal’s disposition allows restart (for example when SA_RESTART is in effect). It is part of the kernel’s mechanism for restartable system calls and is primarily an internal signal-handling aid.

When a process is executing a blocking system call and a signal is delivered, the kernel may return -ERESTARTSYS to indicate that the call can be automatically restarted. Whether the system call is actually restarted depends on the signal handler’s flags and the kernel’s restart policy for the affected syscall. If SA_RESTART is set for the signal, many blocking syscalls are resumed by retrying the call; if not, the syscall may terminate with an error such as EINTR.

In user space, ERESTARTSYS is largely an implementation detail of the kernel and C library. Glibc and other libraries usually handle restartable behavior by automatically retrying eligible syscalls when SA_RESTART is enabled, so applications may not observe ERESTARTSYS directly. In some debugging or low-level contexts, the kernel’s internal ERESTARTSYS code paths may appear in traces or in kernel logs, but ordinary programs typically see EINTR for interrupted syscalls unless automatic restart is performed.

Compatibility and scope: ERESTARTSYS is Linux-specific and tied to the kernel’s restartable syscall feature. It is distinct from the more widely exposed errno value EINTR, which represents an interrupt without automatic restart. The exact behavior can vary by architecture and kernel version, and not all syscalls are restartable.

See also: EINTR, ERESTARTNOINTR, SA_RESTART.