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sync(2)                       System Calls Manual                      sync(2)

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  contain-
       ing 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 sys-
       tem 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 re-
       turning.

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

Linux man-pages 6.03              2023-02-05                           sync(2)

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