cp without overwriting destination permissions

Question

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.

Answer 1

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

Answer 2

cat will work, too:

cat /tmp/file > /home/file

Answer 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

Answer 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

Answer 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

Answer 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