关于该工具有两个man页面：sync
(1) http://man7.org/linux/man-pages/man1/sync.1.html
NAME
sync - Synchronize cached writes to persistent storage
SYNOPSIS top
sync [OPTION] [FILE]...
DESCRIPTION top
Synchronize cached writes to persistent storage
If one or more files are specified, sync only them, or their
containing file systems.
-d, --data
sync only file data, no unneeded metadata
-f, --file-system
sync the file systems that contain the files
--help display this help and exit
--version
output version information and exit
(2) http://manpages.ubuntu.com/manpages/trusty/en/man8/sync.8.html
NAME
sync - synchronize data on disk with memory
SYNOPSIS
sync [--help] [--version]
DESCRIPTION
sync writes any data buffered in memory out to disk. This can include
(but is not limited to) modified superblocks, modified inodes, and
delayed reads and writes. This must be implemented by the kernel; The
sync program does nothing but exercise the sync(2) system call.
The kernel keeps data in memory to avoid doing (relatively slow) disk
reads and writes. This improves performance, but if the computer
crashes, data may be lost or the filesystem corrupted as a result.
sync ensures that everything in memory is written to disk.
sync should be called before the processor is halted in an unusual
manner (e.g., before causing a kernel panic when debugging new kernel
code). In general, the processor should be halted using the
shutdown(8) or reboot(8) or halt(8) commands, which will attempt to put
the system in a quiescent state before calling sync(2). (Various
implementations of these commands exist; consult your documentation; on
some systems one should not call reboot(8) and halt(8) directly.)
第一个来自coreutils，第二个来自fileutils。我尝试sync从 Ubuntu 14.04 中编译该工具，coreutils 8.29但得到的结果与sync(2) 相同。
如何sync在 Ubuntu 14.04 上获得具有功能 (1) 的工具？