Red Hat commands and tips (Part1)

Red Hat commands and tips (Part1)

There are many commands on Linux and many different ways of doing things.
There are some commands which are important to know and ways of piping them to give you a best result.

I am going to cover some commands which I find interesting and how to best use them.

I would like to point out that some of these commands you will be able to use in any distro, but some are Red Hat/Centos/Fedore specific.

Check which services are enables on runlevel 3
[root@centos63 ~]# chkconfig --list | grep 3:on
auditd          0:off   1:off   2:on    3:on    4:on    5:on    6:off
crond           0:off   1:off   2:on    3:on    4:on    5:on    6:off
ip6tables       0:off   1:off   2:on    3:on    4:on    5:on    6:off
iptables        0:off   1:off   2:on    3:on    4:on    5:on    6:off
Check services on runlevel 3, output process name and runlevel 3
[root@centos63 ~]# chkconfig --list | grep 3:on | awk '{print $1,$5}'
auditd 3:on
crond 3:on
ip6tables 3:on
iptables 3:on
lvm2-monitor 3:on
Disable service (smb - samba) from runlevel 3
[root@centos63 ~]# chkconfig --level 3 smb off

Enable service to start on runlevel 3
[root@centos63 ~]# chkconfig --level 3 smb on

Start, Stop and re-start services
[Start]
[root@centos63 ~]# service smb start
Starting SMB services:                                     [  OK  ]
[Stop]
[root@centos63 ~]# service smb stop
Shutting down SMB services:                                [  OK  ]
[Re-start]
[root@centos63 ~]# service smb restart
Shutting down SMB services:                                [  OK  ]
Starting SMB services:                                     [  OK  ]
Find the IP addresses of your Linux server (only IPs)
[root@centos63 ~]#ifconfig | grep "inet addr" | awk '{print $2}' | cut -d : -f 2
192.168.1.34
127.0.0.1
How to bring eth0 interface down
[root@centos63 ~]# ifdown eth0
Note: Be careful if you are logged via SSH, it will drop the connection.

How to bring eth0 interface up
[root@centos63 ~]# ifup eth0

How to set a default Gateway
[root@centos63 ~]# route add default gw 192.168.1.1

How to delete a default gateway
[root@centos63 ~]# route del default gw 192.168.1.1
How to add a static route to netwotk 192.168.3.0/24
[root@centos63~]# route add -net 192.168.3.0 netmask 255.255.255.0 gw 192.168.1.1

Check File System usage (human readable)
[root@centos63 ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
                       47G  1.1G   44G   3% /
tmpfs                 499M     0  499M   0% /dev/shm
/dev/sda1             485M   52M  408M  12% /boot

Check free memory
[root@centos63 ~]# free -m
             total       used       free     shared    buffers     cached
Mem:           996        121        875          0          7         44
-/+ buffers/cache:         69        927
Swap:         2015          0       2015
Check all running processes
[root@centos63 ~]# ps -eaf
UID        PID  PPID  C STIME TTY          TIME CMD
root         1     0  0 20:40 ?        00:00:01 /sbin/init
root         2     0  0 20:40 ?        00:00:00 [kthreadd]
root         3     2  0 20:40 ?        00:00:00 [migration/0]
root         4     2  0 20:40 ?        00:00:00 [ksoftirqd/0]
root      1207  1054  0 21:53 ?        00:00:00 sshd: root@pts/0
root      1209  1207  0 21:54 pts/0    00:00:00 -bash
root      1288     1  0 22:09 ?        00:00:00 smbd -D
root      1290  1288  0 22:10 ?        00:00:00 smbd -D
root      1373  1163  0 22:20 tty1     00:00:00 -bash
postfix   1447  1131  0 22:20 ?        00:00:00 pickup -l -t fifo -u
Check if specific process is running
[root@centos63 ~]# ps -eaf | grep smb
root      1288     1  0 22:09 ?        00:00:00 smbd -D
root      1290  1288  0 22:10 ?        00:00:00 smbd -D
root      1461  1209  0 22:31 pts/0    00:00:00 grep smb
Check all open TCP ports on your Server
[root@centos63 ~]# netstat -ant
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address               Foreign Address             State
tcp        0      0 127.0.0.1:199               0.0.0.0:*                   LISTEN
tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN
tcp        0      0 127.0.0.1:25                0.0.0.0:*                   LISTEN
tcp        0     52 192.168.1.34:22             192.168.1.33:55348          ESTABLISHED
tcp        0      0 :::139                      :::*                        LISTEN
tcp        0      0 :::22                       :::*                        LISTEN
tcp        0      0 :::445                      :::*                        LISTEN
There are many very useful commands, these a just some of the commands and combinations I use.
If you found this useful, let me know and I will write some more useful commands to share with you.

Hope you have enjoyed.

by Renato de Oliveira