Chown only where needed / speedup chown

When you use chown in a manner that changes only the group, then it acts the same as chgrp. The owner of a file or directory can change the group to any group he is a member of.

It works like that because both the chown and chgrp commands use the same underlying chown syscall, which allows changing both owner and group. The syscall is what applies the permission check. The only difference between the chown and chgrp commands is the syntax you use to specify the change you want to make.

Mark can't change the group back to SK001778 because he isn't a member of group SK001778 (and he isn't root, which isn't restricted by group membership).

A simple ls -l would do the trick.

The -l option to the Unix command ls will list the files using a long format. In short this displays for each file:

• Unix file type
• permissions
• number of hard links
• owner
• group
• size
• last-modified date
• filename

Example:

$ ls -l
-rw-------  1 root  root   9560 23 mar 12:05 .bash_history
-rwxr-xr-x  1 root  root    524 28 mai  2007 .bashrc
drwxr-xr-x  3 root  root      3  4 nov 14:51 .cache

From the FreeBSD ls man page (Linux one is a bit scarce):

The Long Format

 If the -l option is given, the following information is displayed for
 each file: file mode, number of links, owner name, group name, MAC label,
 number of bytes in the file, abbreviated month, day-of-month file was
 last modified, hour file last modified, minute file last modified, and
 the pathname.

 If the modification time of the file is more than 6 months in the past or
 future, and the -D or -T are not specified, then the year of the last
 modification is displayed in place of the hour and minute fields.

 If the owner or group names are not a known user or group name, or the -n
 option is given, the numeric ID's are displayed.

 If the file is a character special or block special file, the device num-
 ber for the file is displayed in the size field.  If the file is a sym-
 bolic link the pathname of the linked-to file is preceded by ``->''.

 The listing of a directory's contents is preceded by a labeled total num-
 ber of blocks used in the file system by the files which are listed as
 the directory's contents (which may or may not include . and .. and other
 files which start with a dot, depending on other options).

 The default block size is 512 bytes.  The block size may be set with
 option -k or environment variable BLOCKSIZE.  Numbers of blocks in the
 output will have been rounded up so the numbers of bytes is at least as
 many as used by the corresponding file system blocks (which might have a
 different size).

 The file mode printed under the -l option consists of the entry type and
 the permissions.  The entry type character describes the type of file, as
 follows:

To know more:

• wikipedia about ls
• man ls on FreeBSD (with a nice part about the Long Format)
• info ls on your GNU/Linux system