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 versions <= 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 5.10 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/.