sync(2) - Linux manual page (original) (raw)

sync(2) System Calls Manual sync(2)

NAME top

   sync, syncfs - commit filesystem caches to disk

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#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 top

   **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 top

   **syncfs**() returns 0 on success; on error, it returns -1 and sets
   _[errno](../man3/errno.3.html)_ to indicate the error.

ERRORS top

   **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)](../man2/write.2.html)
          system call, and some previous write failed due to
          insufficient storage space.

VERSIONS top

   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 top

   **sync**() POSIX.1-2008.

   **syncfs**()
          Linux.

HISTORY top

   **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 top

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

SEE ALSO top

   [sync(1)](../man1/sync.1.html), [fdatasync(2)](../man2/fdatasync.2.html), [fsync(2)](../man2/fsync.2.html)

COLOPHON top

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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)