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

       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.

STANDARDS

       sync() POSIX.1-2008.

       syncfs()
              Linux.

HISTORY

       sync() POSIX.1-2001, SVr4, 4.3BSD.

       syncfs()
              Linux 2.6.39, glibc 2.14.

       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.

       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)

Linux man-pages 6.9.1                              2024-05-02                                            sync(2)