sync

SYNC(2)                     Linux Programmer's Manual                    SYNC(2)



NAME
       sync, syncfs - commit filesystem caches 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():
           _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 files 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 to
       glibc in version 2.14.

CONFORMING TO
       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 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 version 1.3.20 Linux did not wait for I/O to complete before
       returning.

SEE ALSO
       sync(1), fdatasync(2), fsync(2)

COLOPHON
       This page is part of release 5.11 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)