sync(8) [centos man page]

SYNC(8) 						     Linux Programmer's Manual							   SYNC(8)

NAME

       sync - synchronize data on disk with memory

SYNOPSIS

       sync [--help] [--version]

DESCRIPTION

       sync  writes  any data buffered in memory out to disk.  This can include (but is not limited to) modified superblocks, modified inodes, and
       delayed reads and writes.  This must be implemented by the kernel; The sync program does nothing but exercise the sync(2) system call.

       The kernel keeps data in memory to avoid doing (relatively slow) disk reads and writes.	This improves performance,  but  if  the  computer
       crashes, data may be lost or the file system corrupted as a result.  sync ensures that everything in memory is written to disk.

       sync  should  be  called before the processor is halted in an unusual manner (e.g., before causing a kernel panic when debugging new kernel
       code).  In general, the processor should be halted using the shutdown(8) or reboot(8) or halt(8) commands, which will attempt  to  put  the
       system  in a quiescent state before calling sync(2).  (Various implementations of these commands exist; consult your documentation; on some
       systems one should not call reboot(8) and halt(8) directly.)

OPTIONS

       --help Print a usage message on standard output and exit successfully.

       --version
	      Print version information on standard output, then exit successfully.

       --     Terminate option list.

ENVIRONMENT

       The variables LANG, LC_ALL, LC_CTYPE, and LC_MESSAGES have the usual meaning.

CONFORMING TO

       POSIX.2.

NOTES

       On Linux, sync is guaranteed only to schedule the dirty blocks for writing; it can actually take a short time before  all  the  blocks  are
       finally written.  The reboot(8) and halt(8) commands take this into account by sleeping for a few seconds after calling sync(2).

       This page describes sync as found in the fileutils-4.0 package; other versions may differ slightly.

SEE ALSO

       sync(2), halt(8), reboot(8), update(8)

COLOPHON

       This  page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    1998-11-01								   SYNC(8)

Check Out this Related Man Page

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

NAME

       sync, syncfs - commit buffer cache 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():
	   _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

       syncfs():
	   _GNU_SOURCE

DESCRIPTION

       sync() causes all buffered modifications to file metadata and data to be written to the underlying file systems.

       syncfs() is like sync(), but synchronizes just the file system 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 reason:

       EBADF  fd is not a valid file descriptor.

VERSIONS

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

CONFORMING TO

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

       syncfs() is Linux-specific.

NOTES

       Since  glibc  2.2.2  the  Linux prototype for sync() is as listed above, following the various standards.  In libc4, libc5, and glibc up to
       2.2.1 it was "int sync(void)", and sync() always returned 0.

BUGS

       According to the standard specification (e.g., POSIX.1-2001), sync() schedules the writes, but may return  before  the  actual  writing	is
       done.   However,  since	version  1.3.20  Linux does actually wait.  (This still does not guarantee data integrity: modern disks have large
       caches.)

SEE ALSO

       bdflush(2), fdatasync(2), fsync(2), sync(8), update(8)

COLOPHON

       This page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2012-05-04								   SYNC(2)

Linux and UNIX Man Pages

sync(8) [centos man page]

Check Out this Related Man Page