sync

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

NAME
       sync, syncfs - commit filesystem caches to disk

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 versions <= 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  contain-
       ing 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 files 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
       syncfs()  first  appeared in Linux 2.6.39; library support was added to
       glibc in version 2.14.

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

       syncfs() is Linux-specific.

NOTES
       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 sys-
       tem 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
       Before version 1.3.20 Linux did not wait for I/O to complete before re-
       turning.

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

COLOPHON
       This page is part of release 5.10 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
       https://www.kernel.org/doc/man-pages/.

Linux                             2020-08-13                           SYNC(2)