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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
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SYNC(2) Linux Programmer's Manual SYNC(2)
sync, syncfs - commit filesystem caches to disk
#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 <= 2.19: */ _BSD_SOURCE
syncfs():
_GNU_SOURCE
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.
syncfs() returns 0 on success; on error, it returns -1 and sets
errno to indicate the error.
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 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.
syncfs() first appeared in Linux 2.6.39; library support was
added to glibc in version 2.14.
sync(): POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
syncfs() is Linux-specific.
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.
Before version 1.3.20 Linux did not wait for I/O to complete
before returning.
sync(1), fdatasync(2), fsync(2)
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
https://www.kernel.org/doc/man-pages/.
Linux 2021-03-22 SYNC(2)
Pages that refer to this page: sync(1), systemd-nspawn(1), bdflush(2), fsync(2), mount(2), reboot(2), sync_file_range(2), syscalls(2), fclose(3), fflush(3), nfs(5), ctrlaltdel(8), fdisk(8), fsck.minix(8), mke2fs(8), mount(8), xfs_io(8), xfs_quota(8)
Copyright and license for this manual page
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