Thursday, December 31, 2009

FILE TYPES-PERMISSIONS-SYMLINKS IN REDHAT LINUX

FILE TYPES-PERMISSIONS-SYMLINKS

Features:
1. The ability to restrict/control access to files

Note:

• 10 bits represent permissions for files (including directories)

• use 'ls -l' to examine permissions or GUI application like 'Nautilus'

-rwxrwxr-x 1 linuxcbt linuxcbt 681 Jan 13 11:31 regextest.pl

• 1st bit = file type. '-' = file, 'd' = directory

• 2nd - 4th bits = owner's permissions

• r = read = 4

• w = write = 2

• x = execute = 1

• -= none = 0

• 5th - 7th bits = group owner's permissions

• r = read = 4

• w = write = 2

• x = execute = 1

• -= none = 0

• 8th - 10th bits = everyone (world)

• r = read = 4

• w = write = 2

• x = execute = 1

• -= none = 0

Task:

1. Manipulate file permissions using 'chmod'

• chmod -x regextest.pl

• -rw-rw-r-- 1 linuxcbt linuxcbt 681 Jan 13 11:31 regextest.pl

• rw = 6 or 4+2 for owner

• rw = 6 or 4+2 for group owner

• r = 4 for everyone else (world)

• Octal notation: 664 for file 'regexetest.pl'

• chmod 664 regextest.pl - removes execution for ALL users

• chmod 775 regextest.pl - enables execution for ALL users


2. Ensure that 'regextest.pl' is rw by owner and noone else

• chmod 600 regextest.pl

Note: File will now be rw by owner (linuxcbt) and 'root'

3. Ensure that 'regextest.pl' is r by owner and noone else

• chmod 400 regextest.pl && ls -l regextest.pl

Note: chmod supports string values, which represent octal values

• chmod +/- x file

• chmod +/- w file

• chmod +/- r file

• chmod +/- u+x file - updates owner's execute permissions on the file

• chmod +/- o+x file - updates other's execute permissions on the file

• chmod +/- g+x file - updates group's execute permissions on the file

• chmod a+rwx = chmod 777

• chown - permits changing of ownership of files

chown root regextest.pl - changes ownership to 'root'

chown linuxcbt:sales regextest.pl - changes owner and group to
'linuxcbt:sales'

Task:

Update 'regextest.pl' so that owner and group owner may modify the file

• chmod 660 regextest.pl

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