sync(2) — Linux manual page

sync(2)                    System Calls Manual                   sync(2)

NAME

       sync, syncfs - commit filesystem caches to disk

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <unistd.h>

       void sync(void);

       int syncfs(int fd);

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       sync():
           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE

       syncfs():
           _GNU_SOURCE

DESCRIPTION

       sync() causes all pending modifications to filesystem metadata
       and cached file data to be written to the underlying filesystems.

       syncfs() is like sync(), but synchronizes just the filesystem
       containing file referred to by the open file descriptor fd.

RETURN VALUE

       syncfs() returns 0 on success; on error, it returns -1 and sets
       errno to indicate the error.

ERRORS

       sync() is always successful.

       syncfs() can fail for at least the following reasons:

       EBADF  fd is not a valid file descriptor.

       EIO    An error occurred during synchronization.  This error may
              relate to data written to any file on the filesystem, or
              on metadata related to the filesystem itself.

       ENOSPC Disk space was exhausted while synchronizing.

       ENOSPC
       EDQUOT Data was written to a file on NFS or another filesystem
              which does not allocate space at the time of a write(2)
              system call, and some previous write failed due to
              insufficient storage space.

VERSIONS

       According to the standard specification (e.g., POSIX.1-2001),
       sync() schedules the writes, but may return before the actual
       writing is done.  However Linux waits for I/O completions, and
       thus sync() or syncfs() provide the same guarantees as fsync()
       called on every file in the system or filesystem respectively.

STANDARDS

       sync() POSIX.1-2008.

       syncfs()
              Linux.

HISTORY

       sync() POSIX.1-2001, SVr4, 4.3BSD.

       syncfs()
              Linux 2.6.39, glibc 2.14.

       Since glibc 2.2.2, the Linux prototype for sync() is as listed
       above, following the various standards.  In glibc 2.2.1 and
       earlier, it was "int sync(void)", and sync() always returned 0.

       In mainline kernel versions prior to Linux 5.8, syncfs() will
       fail only when passed a bad file descriptor (EBADF).  Since Linux
       5.8, syncfs() will also report an error if one or more inodes
       failed to be written back since the last syncfs() call.

BUGS

       Before Linux 1.3.20, Linux did not wait for I/O to complete
       before returning.

SEE ALSO

       sync(1), fdatasync(2), fsync(2)

COLOPHON

       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-6.9.1.tar.gz
       fetched from
       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
       2024-06-26.  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 6.9.1          2024-05-02                        sync(2)

Pages that refer to this page: sync(1), systemd-nspawn(1), bdflush(2), fsync(2), mount(2), reboot(2), sync_file_range(2), syscalls(2), fclose(3), fflush(3), nfs(5), ctrlaltdel(8), fdisk(8), fsck.minix(8), mke2fs(8), mount(8), xfs_io(8), xfs_quota(8)

---