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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 filesystems.

syncfs() is like sync(), but synchronizes just the filesystem 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 glibc 2.2.1 and earlier, 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(1)

Colophon

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