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【整理】Linux命令中:rsync和cp之间的区别

Linux crifan 3007浏览 0评论

【背景】

折腾:

【记录】尝试分析Buildroot在make menuconfig后make时的内部执行逻辑

期间,通过:

【整理】Linux命令rsync的用法

而了解到了rsync的功能:

大概就是,相当于,从源,到目的,拷贝文件,并且可以设置参数,保持很多文件和文件夹的属性。

感觉和cp很类似。

所以想要搞清楚,rsync和cp的区别。

【折腾过程】

1.参考:

Copy or rsync command

的解释是:

其中一人的解释:

对于拷贝文件,实现备份的话,rsync,比cp更好。

因为rsync只拷贝那些改动了的内容。

2.另外的解释,貌似更合理:

rsync未必是最好。取决于实际情况。

比如:

当拷贝的源和目标,内容很大,而差异很小,则用

cp -u

会更有效。

3.所以先去看看cp的用法:

CLi@PC-CLI-1 ~/develop/buildroot/buildroot-2013.05
$ cp --help
Usage: cp [OPTION]... [-T] SOURCE DEST
  or:  cp [OPTION]... SOURCE... DIRECTORY
  or:  cp [OPTION]... -t DIRECTORY SOURCE...
Copy SOURCE to DEST, or multiple SOURCE(s) to DIRECTORY.

Mandatory arguments to long options are mandatory for short options too.
  -a, --archive                same as -dR --preserve=all
      --attributes-only        don't copy the file data, just the attributes
      --backup[=CONTROL]       make a backup of each existing destination file
  -b                           like --backup but does not accept an argument
      --copy-contents          copy contents of special files when recursive
  -d                           same as --no-dereference --preserve=links
  -f, --force                  if an existing destination file cannot be
                                 opened, remove it and try again (redundant if
                                 the -n option is used)
  -i, --interactive            prompt before overwrite (overrides a previous -n
                                  option)
  -H                           follow command-line symbolic links in SOURCE
  -l, --link                   hard link files instead of copying
  -L, --dereference            always follow symbolic links in SOURCE
  -n, --no-clobber             do not overwrite an existing file (overrides
                                 a previous -i option)
  -P, --no-dereference         never follow symbolic links in SOURCE
  -p                           same as --preserve=mode,ownership,timestamps
      --preserve[=ATTR_LIST]   preserve the specified attributes (default:
                                 mode,ownership,timestamps), if possible
                                 additional attributes: context, links, xattr,
                                 all
      --no-preserve=ATTR_LIST  don't preserve the specified attributes
      --parents                use full source file name under DIRECTORY
  -R, -r, --recursive          copy directories recursively
      --reflink[=WHEN]         control clone/CoW copies. See below
      --remove-destination     remove each existing destination file before
                                 attempting to open it (contrast with --force)
      --sparse=WHEN            control creation of sparse files. See below
      --strip-trailing-slashes  remove any trailing slashes from each SOURCE
                                 argument
  -s, --symbolic-link          make symbolic links instead of copying
  -S, --suffix=SUFFIX          override the usual backup suffix
  -t, --target-directory=DIRECTORY  copy all SOURCE arguments into DIRECTORY
  -T, --no-target-directory    treat DEST as a normal file
  -u, --update                 copy only when the SOURCE file is newer
                                 than the destination file or when the
                                 destination file is missing
  -v, --verbose                explain what is being done
  -x, --one-file-system        stay on this file system
      --help     display this help and exit
      --version  output version information and exit

By default, sparse SOURCE files are detected by a crude heuristic and the
corresponding DEST file is made sparse as well.  That is the behavior
selected by --sparse=auto.  Specify --sparse=always to create a sparse DEST
file whenever the SOURCE file contains a long enough sequence of zero bytes.
Use --sparse=never to inhibit creation of sparse files.

When --reflink[=always] is specified, perform a lightweight copy, where the
data blocks are copied only when modified.  If this is not possible the copy
fails, or if --reflink=auto is specified, fall back to a standard copy.

The backup suffix is `~', unless set with --suffix or SIMPLE_BACKUP_SUFFIX.
The version control method may be selected via the --backup option or through
the VERSION_CONTROL environment variable.  Here are the values:

  none, off       never make backups (even if --backup is given)
  numbered, t     make numbered backups
  existing, nil   numbered if numbered backups exist, simple otherwise
  simple, never   always make simple backups

As a special case, cp makes a backup of SOURCE when the force and backup
options are given and SOURCE and DEST are the same name for an existing,
regular file.

Report cp bugs to bug-coreutils@gnu.org
GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
General help using GNU software: <http://www.gnu.org/gethelp/>
For complete documentation, run: info coreutils 'cp invocation'

CLi@PC-CLI-1 ~/develop/buildroot/buildroot-2013.05
$

得知-u是update,更新的意思,只更新SOURCE中更新的内容,或者是目标中缺失的文件:

对于文件备份来说,已经足够用了:

每次备份,的确只要备份:

要么是内容更新

要么是原先没有(缺失的)文件

即可。

4.再参考了:

Use Rsync Instead of Cp

后,更加推荐用rsync了:

rsync可以显示进度条(虽然不是很完美):对于拷贝大量文件,还是很有用的。

其举了个例子:

rsync -a --stats --progress /home/tim/stuff /home/tim/documents

而还支持ssh:

rsync -a --stats --progress /home/tim/stuff tim@foo.example.com:/home/tim/

或:

rsync -a --stats --progress tim@foo.example.com:/home/tim/stuff /home/tim/

5.另外有空也可以参考:

A Tutorial on Using rsync

 

【总结】

rsync:只拷贝那些更新的文件;

cp -u:也可以实现类似效果;

两者都基本可以满足备份的需求;

只是一般情况下,用rsync做这类备份之类的事情,更多见;

总体来说:

备份文件,更推荐用rsync。

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