7 Useful Linux Utilities

There are 7 useful linux utilities that you must install on new linux server. Most Linux distributions are equipped with tons of linux command utility, but if you have installed minimal operating system, all these software will not exist. These tools will very useful in your troubleshooting and will help to find possible causes of a problem. Most of the utilities have the same function in CentOS or Red Hat Enterprise Linux (RHEL). You can easily identify whether the utility installed on your linux operating system or not. You will see one or more below warning :

[root@rhel62 ~]# wget
-bash: wget: command not found

[root@rhel62 ~]# telnet
-bash: telnet: command not found

[root@rhel62 ~]# scp
-bash: scp: command not found

[root@rhel62 ~]# man scp
-bash: man: command not found

[root@rhel62 ~]# nslookup
-bash: nslookup: command not found

[root@rhel62 ~]# dig
-bash: dig: command not found

[root@rhel62 ~]# host
-bash: host: command not found

1. What is wget ?
Wget is a network utility to retrieve files from the Web using http and ftp, the two most widely used Internet protocols.
Example :

[root@rhel62 ~]# wget http://files2.zimbra.com/downloads/8.0.2_GA/zcs-8.0.2_GA_5569.RHEL6_64.20121210115059.tgz

2. What is telnet ?
Telnet is a network protocol used on the Internet or local area networks. Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers and very useful for troubleshooting and verify the opened ports.
Example :

[root@rhel62 ~]# telnet localhost 25
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 rhel62.ehowstuff.local ESMTP Postfix

3. What is scp ?
scp also call secure copy, is remote file copy utility between hosts on a network. It uses ssh for data transfer and provides the same authentication and same level of security as ssh.
Example :

[root@rhel62 ~]# scp root@192.168.2.60:/tmp/VMwareTools-9.2.2-893683.tar.gz .
The authenticity of host '192.168.2.60 (192.168.2.60)' can't be established.
RSA key fingerprint is 76:78:87:36:44:c1:46:fa:c4:b4:61:4a:e5:b3:be:e3.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.2.60' (RSA) to the list of known hosts.
root@192.168.2.60's password:
VMwareTools-9.2.2-893683.tar.gz                                                       100%   63MB  63.3MB/s   00:01

4. What is man ?
man is used to display the manual page for other commands It’s help to explain the functions for the commands that commonly used. The term “man” is short for manual.
Example :

[root@rhel62 ~]# man wget

WGET(1)                            GNU Wget                            WGET(1)

NAME
       Wget - The non-interactive network downloader.

SYNOPSIS
       wget [option]... [URL]...

DESCRIPTION
       GNU Wget is a free utility for non-interactive download of files from the Web.  It supports HTTP,
       HTTPS, and FTP protocols, as well as retrieval through HTTP proxies.

       Wget is non-interactive, meaning that it can work in the background, while the user is not logged on.
       This allows you to start a retrieval and disconnect from the system, letting Wget finish the work.
       By contrast, most of the Web browsers require constant userâs presence, which can be a great
       hindrance when transferring a lot of data.

       Wget can follow links in HTML, XHTML, and CSS pages, to create local versions of remote web sites,
       fully recreating the directory structure of the original site.  This is sometimes referred to as
       "recursive downloading."  While doing that, Wget respects the Robot Exclusion Standard (/robots.txt).
       Wget can be instructed to convert the links in downloaded files to point at the local files, for
       offline viewing.

5. What is nslookup, dig, host ?
nslookup, dig and host are part of the bind utilities.These utilities are the basic tools for DNS client and DNS server troubleshooting.
Examples :

[root@rhel62 ~]# nslookup
> set type=mx
> ehowstuff.com
Server:         8.8.8.8
Address:        8.8.8.8#53

Non-authoritative answer:
ehowstuff.com   mail exchanger = 0 ehowstuff.com.

Authoritative answers can be found from:
>

[root@rhel62 ~]# dig ehowstuff.com

; < <>> DiG 9.7.3-P3-RedHat-9.7.3-8.P3.el6 < <>> ehowstuff.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER< <- opcode: QUERY, status: NOERROR, id: 4273
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;ehowstuff.com.                 IN      A

;; ANSWER SECTION:
ehowstuff.com.          14400   IN      A       184.173.214.97

;; Query time: 272 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Tue Mar 12 21:41:50 2013
;; MSG SIZE  rcvd: 47

[root@rhel62 ~]# host -t mx ehowstuff.com
ehowstuff.com mail is handled by 0 ehowstuff.com.

How to install wget, scpt, telnet, man, nslookup, dig and host utilities ?
Simply run the following commands :

[root@rhel62 ~]# yum install wget telnet openssh-clients bind-utils man -y