sync(2) — Linux manual page


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

NAME         top

       sync, syncfs - commit filesystem caches to disk

SYNOPSIS         top

       #include <unistd.h>

       void sync(void);

       int syncfs(int fd);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE


DESCRIPTION         top

       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         top

       syncfs() returns 0 on success; on error, it returns -1 and sets errno
       to indicate the error.

ERRORS         top

       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.

              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

VERSIONS         top

       syncfs() first appeared in Linux 2.6.39; library support was added to
       glibc in version 2.14.

CONFORMING TO         top

       sync(): POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

       syncfs() is Linux-specific.

NOTES         top

       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         top

       Before version 1.3.20 Linux did not wait for I/O to complete before

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.09 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

Linux                            2020-08-13                          SYNC(2)

Pages that refer to this page: sync(1)arm_sync_file_range(2)bdflush(2)fdatasync(2)fsync(2)mount(2)reboot(2)sync_file_range2(2)sync_file_range(2)syscalls(2)fclose(3)fflush(3)nfs(5)ctrlaltdel(8)fsck.minix(8)mke2fs(8)mount(8)xfs_io(8)xfs_quota(8)