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 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 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 system 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 returning.

SEE ALSO

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