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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | NOTES | SEE ALSO | COLOPHON |
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get_robust_list(2) System Calls Manual get_robust_list(2)
get_robust_list, set_robust_list - get/set list of robust futexes
Standard C library (libc, -lc)
#include <linux/futex.h> /* Definition of struct robust_list_head */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
long syscall(SYS_get_robust_list, int pid,
struct robust_list_head **head_ptr, size_t *sizep);
long syscall(SYS_set_robust_list,
struct robust_list_head *head, size_t size);
Note: glibc provides no wrappers for these system calls,
necessitating the use of syscall(2).
These system calls deal with per-thread robust futex lists. These
lists are managed in user space: the kernel knows only about the
location of the head of the list. A thread can inform the kernel
of the location of its robust futex list using set_robust_list().
The address of a thread's robust futex list can be obtained using
get_robust_list().
The purpose of the robust futex list is to ensure that if a thread
accidentally fails to unlock a futex before terminating or calling
execve(2), another thread that is waiting on that futex is
notified that the former owner of the futex has died. This
notification consists of two pieces: the FUTEX_OWNER_DIED bit is
set in the futex word, and the kernel performs a futex(2)
FUTEX_WAKE operation on one of the threads waiting on the futex.
The get_robust_list() system call returns the head of the robust
futex list of the thread whose thread ID is specified in pid. If
pid is 0, the head of the list for the calling thread is returned.
The list head is stored in the location pointed to by head_ptr.
The size of the object pointed to by **head_ptr is stored in
sizep.
Permission to employ get_robust_list() is governed by a ptrace
access mode PTRACE_MODE_READ_REALCREDS check; see ptrace(2).
The set_robust_list() system call requests the kernel to record
the head of the list of robust futexes owned by the calling
thread. The head argument is the list head to record. The size
argument should be sizeof(*head).
The set_robust_list() and get_robust_list() system calls return
zero when the operation is successful, an error code otherwise.
The set_robust_list() system call can fail with the following
error:
EINVAL size does not equal sizeof(struct robust_list_head).
The get_robust_list() system call can fail with the following
errors:
EFAULT The head of the robust futex list can't be stored at the
location head.
EPERM The calling process does not have permission to see the
robust futex list of the thread with the thread ID pid, and
does not have the CAP_SYS_PTRACE capability.
ESRCH No thread with the thread ID pid could be found.
These system calls were added in Linux 2.6.17.
These system calls are not needed by normal applications.
A thread can have only one robust futex list; therefore
applications that wish to use this functionality should use the
robust mutexes provided by glibc.
In the initial implementation, a thread waiting on a futex was
notified that the owner had died only if the owner terminated.
Starting with Linux 2.6.28, notification was extended to include
the case where the owner performs an execve(2).
The thread IDs mentioned in the main text are kernel thread IDs of
the kind returned by clone(2) and gettid(2).
futex(2), pthread_mutexattr_setrobust(3)
Documentation/robust-futexes.txt and
Documentation/robust-futex-ABI.txt in the Linux kernel source tree
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 get_robust_list(2)
Pages that refer to this page: execve(2), futex(2), gettid(2), ptrace(2), syscalls(2), exit(3), pthread_mutexattr_setrobust(3), capabilities(7), futex(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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