LINUX
COMMANDS
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Access rights
Every user belongs to atleast one group, their login
group - given the same name as their user account.
Every file belongs to an owner and group. Usually the user
that created the file and that user's login group. To display
the owner and group a file belongs to, enter:
ls -l
...and examine the third (owner) and fourth (group) columns:
-rw-rw-r-- 1 john john 10760 Nov
20 16:50 report.txt
$ groups
groups
Display groups you belong to.
groups john
Display groups john belongs to.
# chgrp - change group
chgrp john report.txt
Change group of file report.txt, to john.
chgrp -R john .
Change group of all files and subdirectories (i.e. -R
for recursively) in the current (.) directory,
to john.
# chown - change owner
chown john report.txt
Change owner of file report.txt, to john.
chown -R john .
Change owner of all files and subdirectories (i.e. -R
for recursively) in the current (.) directory,
to john.
chown -R john:john .
Change owner and group (owner:group)
of all files and subdirectories (i.e. -R for recursively)
in the current (.) directory, to john.
$ chmod - change mode
Entering ls -l will display in the first column,
the permissions for each file and directory, in the current
directory.
For example:
-rw-rw-r-- 1 john john 10760 Nov
20 16:50 report.txt
Here's how it breaks down:
| Type |
Owner |
Group |
Other |
| - |
rw- |
rw- |
r-- |
Type
| Character |
Description |
| - |
Normal file. |
| d |
Directory. |
| l |
Symbolic link. |
Owner, group, and other
The owner, group, and other sections,
each have three entries: r (read); w (write);
x (execute)
An r, w, or x, means that permission
is given, a hypen (-) means it isn't. For example:
-rw-rw-r--
...indicates a normal file, with read/write but no execute
permissions given to the owner and group, and all other
users just have read permission.
Setting permissions: method one
| Example |
Description |
| chmod +r report.txt |
Give read permission to all. |
| chmod -r report.txt |
Remove read permission from all. |
| chmod =r report.txt |
Give nothing but read permission to all. |
| chmod +w report.txt |
Give write permission to owner and group. |
| chmod -w report.txt |
Remove write permission from owner and group. |
| chmod =w report.txt |
Give nothing but write permission to owner and group. |
| chmod +x report.txt |
Give execute permission to all. |
| chmod -x report.txt |
Remove execute permission from all. |
| chmod =x report.txt |
Give nothing but execute permission to all. |
In front of any of the above you can add:
| Example |
Short for |
| u |
user |
| g |
group |
| o |
other |
| a |
all (same as: ugo) |
Examples
chmod a+rw report.txt
Give all users read and write permission (what's called
making the file report.txt, world readable
and world writable).
chmod go-w report.txt
Remove write permission (-w) from report.txt
for group and others (go), allowing only the owner
modify the file (as long as they had write permission beforehand).
chmod go= report.txt
Remove all permissions for group and others (go),
making the file report.txt private to owner.
Setting permissions: method two
Permissions can also be set in octal (base 8), where read
permission is a four, write is two, and execute is one.
These you add up separately for user, group and other for
between 000 (---------) and 777
(rwxrwxrwx), like so:
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