sync(2) — Linux manual page


SYNC(2)                 Linux Programmer's Manual                SYNC(2)

NAME         top

       sync, syncfs - commit filesystem caches to disk

SYNOPSIS         top

       #include <unistd.h>

       void sync(void);

       int syncfs(int fd);

   Feature Test Macro Requirements for glibc (see

           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc <= 2.19: */ _BSD_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 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.

              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         top

       syncfs() first appeared in Linux 2.6.39; library support was
       added to glibc in version 2.14.

CONFORMING TO         top

       sync(): POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

       syncfs() is Linux-specific.

NOTES         top

       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.

       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.

       In mainline kernel versions prior to 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 version 1.3.20 Linux did not wait for I/O to complete
       before returning.

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at

Linux                          2021-03-22                        SYNC(2)

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