sync, syncfs - commit filesystem caches to disk
int syncfs(int fd);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_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
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 reason:
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.
- fd is not a valid file descriptor.
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.
Before version 1.3.20 Linux did not wait for I/O to complete before returning.
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