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David
Asked: 2011-05-26 22:55:09 +0800 CST

cp without overwriting destination permissions

  • 772

How do you use the cp command without changing the target file's permissions? For example:

cp /tmp/file   /home/file

I don't want to change chown and chgrp on /home/file.

linux cp

6 Answers

  1. Best Answer

    If you've only opened the manual for cp...

    The next will not overwrite the file permissions and ownership + groupship:

    cp --no-preserve=mode,ownership /tmp/file /home/file

    Note that root privileges are needed if you want to preserve the ownership and groupship.

    An excerpt from the manual:

      --preserve[=ATTR_LIST]
      preserve   the   specified   attributes   (default:  mode,owner-
      ship,timestamps), if possible  additional  attributes:  context,
      links, xattr, all
    • 37

  2. cat will work, too:

    cat /tmp/file > /home/file
    • 13

  3. By default, GNU cp (version 8.32) will NOT overwrite destination permissions, so the question is moot:

    % ls -li
total 8,192
19392015 -rwxrwxrwx 1 ravi ravi 4 Jan  3 16:54 bar*
19392014 -rw-r--r-- 1 ravi ravi 4 Jan  3 16:46 foo
% cp foo bar
% ls -li
total 8,192
19392015 -rwxrwxrwx 1 ravi ravi 4 Jan  3 16:57 bar*
19392014 -rw-r--r-- 1 ravi ravi 4 Jan  3 16:46 foo
%

    In the case where the destination file is not writable (even though the directory is), cp will say:

    cp: cannot create regular file 'dest-file': Permission denied

    Other options besides cp:

    cat will preserve the inode and permissions of the destination file:

    cat file-with-new-data > file-to-overwrite

    However, redirections won't work with sudo.

    If you want to sudo and keep the destination permissions, use this:

    < file-with-new-data sudo tee file-to-overwrite > /dev/null

    This is equivalent to the more verbose:

    cat file-with-new-data | sudo tee file-to-overwrite > /dev/null
    • 4

  4. Or you can use even better install program from GNU coreutils that has been made for this particular purpose. Please note it is not able to recurse (no -R or -r option).

    http://www.gnu.org/software/coreutils/manual/html_node/install-invocation.html

    • -1

  5. Don't use permission-related switches at all, especially --no-preserve, because it behaves strangely:

    good:

    [il@localhost Downloads]$ sudo cp ssh_host_* /etc/ssh/
[il@localhost Downloads]$ ls -l /etc/ssh
total 604
-rw-r--r--  1 root root     581843 Oct 20  2017 moduli
-rw-r--r--  1 root root       2276 Oct 20  2017 ssh_config
-rw-------  1 root root       3907 Oct 20  2017 sshd_config
-rw-r-----. 1 root ssh_keys    227 Oct  2 12:26 ssh_host_ecdsa_key
-rw-r--r--. 1 root root        172 Oct  2 12:26 ssh_host_ecdsa_key.pub
-rw-r-----. 1 root ssh_keys    411 Oct  2 12:26 ssh_host_ed25519_key
-rw-r--r--. 1 root root        100 Oct  2 12:26 ssh_host_ed25519_key.pub
-rw-r-----. 1 root ssh_keys   1679 Oct  2 12:26 ssh_host_rsa_key
-rw-r--r--. 1 root root        392 Oct  2 12:26 ssh_host_rsa_key.pub

    bad:

    [il@localhost Downloads]$ sudo cp --no-preserve=mode,ownership ssh_host_* /etc/ssh/
[il@localhost Downloads]$ ls -l /etc/ssh
total 604
-rw-r--r--  1 root root     581843 Oct 20  2017 moduli
-rw-r--r--  1 root root       2276 Oct 20  2017 ssh_config
-rw-------  1 root root       3907 Oct 20  2017 sshd_config
-rw-r--r--. 1 root ssh_keys    227 Oct  2 12:27 ssh_host_ecdsa_key
-rw-r--r--. 1 root root        172 Oct  2 12:27 ssh_host_ecdsa_key.pub
-rw-r--r--. 1 root ssh_keys    411 Oct  2 12:27 ssh_host_ed25519_key
-rw-r--r--. 1 root root        100 Oct  2 12:27 ssh_host_ed25519_key.pub
-rw-r--r--. 1 root ssh_keys   1679 Oct  2 12:27 ssh_host_rsa_key
-rw-r--r--. 1 root root        392 Oct  2 12:27 ssh_host_rsa_key.pub
    • -1

  6. The cp doesn't override permissions by default. If you want to make sure permission won't be overridden, use 

    cp --preserve=mode,ownership /tmp/file /target_dir_where_file_resides
    • -1