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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 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  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 reason:
       EBADF  fd is not a valid file descriptor.
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.
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 4.15 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                             2017-09-15                           SYNC(2)