What are the init runlevels defined in Linux?

0 - halt (Do NOT set initdefault to this)

1 - Single user mode

2 - Multiuser, without Network

3 – Text Mode

4 - unused

5 – Graphical Mode

6 - reboot

How to setup NFS?

Edit /etc/exports file before starting the nfs server.

/     IP Address  (rw,no_root_squash)

This will export all files with root r/w to host IP Address

Save your exports file and from the prompt execute exportfs command

Start the nfs server (nfs daemon)

 /etc/rc.d/inid.d/nfs start

How to reboot?

/sbin/shutdown −r now

Which file is used for NTP configuration?

The NTP program is configured using /etc/ntp.conf

How to remove duplicate lines from a sorted file?

Uniq

 

 

 

Which file resolves hostname?

/etc/resolv.conf

 

The kernel configuration  for Tape drive?

 File for device entries is /etc/stinit.def

"stinit"  to  initialize the st (scsi tape) driver.

 

To test the  tape drive configuration ?

> mt -f /dev/nst0 stat

 

 

 

What are the access permission of file/directory?

0 = Nothing
1 = Execute
2 = Write
3 = Execute & Write  (2 + 1)
4 = Read
5 = Execute & Read (4 + 1)
6 = Read & Write (4 + 2)
7 = Execute & Read & Write (4 + 2 + 1)

 

Set user ID, set group ID, sticky bit?

 

In addition to the basic permissions discussed above, there are also three bits of information defined for files in UNIX:

SUID or setuid: change user ID on execution. If setuid bit is set, when the file will be executed by a user, the process will have the same rights as the owner of the file being executed.

SGID or setgid: change group ID on execution. Same as above, but inherits rights of the group of the owner of the file. For directories it also may mean that when a new file is created in the directory it will inherit the group of the directory (and not of the user who created the file).

Sticky bit. It was used to trigger process to "stick" in memory after it is finished, now this usage is obsolete. Currently its use is system dependant and it is mostly used to suppress deletion of the files that belong to other users in the folder where you have "write" access to.

Numeric representation

Octal digit	Binary value	Meaning
0	000	setuid, setgid, sticky bits are cleared
1	001	sticky bit is set
2	010	setgid bit is set
3	011	setgid and sticky bits are set
4	100	setuid bit is set
5	101	setuid and sticky bits are set
6	110	setuid and setgid bits are set
7	111	setuid, setgid, sticky bits are set

Textual representation

SUID	If set, then replaces "x" in the owner permissions to "s", if owner has execute permissions, or to "S" otherwise. Examples: -rws------ both owner execute and SUID are set -r-S------ SUID is set, but owner execute is not set
SGID	If set, then replaces "x" in the group permissions to "s", if group has execute permissions, or to "S" otherwise. Examples: -rwxrws--- both group execute and SGID are set -rwxr-S--- SGID is set, but group execute is not set
Sticky	If set, then replaces "x" in the others permissions to "t", if others have execute permissions, or to "T" otherwise. Examples: -rwxrwxrwt both others execute and sticky bit are set -rwxrwxr-T sticky bit is set, but others execute is not set

 

suid -- this special permission allows the file to be executed with the security permissions of the

file owner instead of the permission of the user who ran the program. This can be a source of security problems. Some daemons run as suid root. The suid permission is seen as an "S" in the user executable position a long directory listing (ls -l). Has no effect if the file is not executable.

To set the suid permission:
chmod u+s filename

sgid -- this special permission allows the file to be run with the security permissions of the group instead of the permission of the user who ran the program. This can be a source of security problems. The sgid permission is seen as an "S" in the group executable position a long directory listing (ls -l). Has no effect if the file is not executable.

To set the sgid permission:

chmod g+s filename