sync
Section: System Calls (2)
Updated: 2023-02-05
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NAME
sync, syncfs - commit filesystem caches to disk
LIBRARY
Standard C library
(libc, -lc)
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 <= 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 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 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.
VERSIONS
syncfs()
first appeared in Linux 2.6.39;
library support was added in glibc 2.14.
STANDARDS
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 system or filesystem respectively.
In mainline kernel versions prior to Linux 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 Linux 1.3.20, Linux did not wait for I/O to complete
before returning.
SEE ALSO
sync(1),
fdatasync(2),
fsync(2)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- STANDARDS
-
- NOTES
-
- BUGS
-
- SEE ALSO
-
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