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

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
On Linux, sync is only guaranteed 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 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at GNU
1998-11-01 SYNC(8)

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

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 Linux 2012-05-04 SYNC(2)
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