How to Change Your Command Prompt in UNIX or Linux

If you do not like your command prompt in UNIX or Linux, you can change it with the export PS1= command. In the example below, I started off with a command prompt of UBUNTU > :

UBUNTU > 

... then I changed it to show the name of the directory I was in. Here is one way to do this:

UBUNTU > export PS1='`pwd` > '
/home/andrew > cd Java
/home/andrew/Java > cd /
/ >

... and here is another:

/ > export PS1='$PWD > '

/ > cd

/home/andrew > cd Java

/home/andrew/Java > 

Finally, I changed it to say Andrew's PC: 

/home/andrew/Java > export PS1="Andrew's PC: "

Andrew's PC:

How to See your IP Address in UBUNTU

You can do this from the Linux prompt as follows. The value you want is in bold. I hope to be using this a lot in future posts:

UBUNTU: ifconfig
eth0      Link encap:Ethernet  HWaddr 00:0c:6e:e7:f1:92 
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Interrupt:19 Base address:0x9800

lo        Link encap:Local Loopback 
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:2102 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2102 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:217564 (217.5 KB)  TX bytes:217564 (217.5 KB)

wlan0     Link encap:Ethernet  HWaddr 00:14:6c:8a:f4:72 
          inet addr:192.168.2.2  Bcast:192.168.2.255  Mask:255.255.255.0
          inet6 addr: fe80::214:6cff:fe8a:f472/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:39507 errors:0 dropped:0 overruns:0 frame:0
          TX packets:37777 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:39342715 (39.3 MB)  TX bytes:7605863 (7.6 MB)

UBUNTU:

ssh Connection refused on UBUNTU

I tried to ssh to localhost on my UBUNTU PC but the connection was refused:

UBUNTU > ssh localhost
ssh: connect to host localhost port 22: Connection refused
UBUNTU >

This was because ssh had not been set up on my machine. I set it up like this:

UBUNTU > sudo apt-get install openssh-server openssh-client
Reading package lists... Done
Building dependency tree    
Reading state information... Done
openssh-client is already the newest version.
Suggested packages:
  rssh molly-guard openssh-blacklist openssh-blacklist-extra monkeysphere
The following NEW packages will be installed
  openssh-server ssh-import-id
0 upgraded, 2 newly installed, 0 to remove and 576 not upgraded.
Need to get 348 kB of archives.
After this operation, 891 kB of additional disk space will be used.
Get:1 http://gb.archive.ubuntu.com/ubuntu/ precise/main openssh-server i386 1:5.9p1-5ubuntu1 [342 kB]
Get:2 http://gb.archive.ubuntu.com/ubuntu/ precise/main ssh-import-id all 2.10-0ubuntu1 [6.598 B]
Fetched 348 kB in 1s (288 kB/s)  
Preconfiguring packages ...
Selecting previously unselected package openssh-server.
(Reading database ... 153823 files and directories currently installed.)
Unpacking openssh-server (from .../openssh-server_1%3a5.9p1-5ubuntu1_i386.deb) ...
Selecting previously unselected package ssh-import-id.
Unpacking ssh-import-id (from .../ssh-import-id_2.10-0ubuntu1_all.deb) ...
Processing triggers for ureadahead ...
ureadahead will be reprofiled on next reboot
me time ...
CreaProcessing triggers for ufw ...
Processing triggers for man-db ...
Setting up openssh-server (1:5.9p1-5ubuntu1) ...
Creating SSH2 RSA key; this may take some time ...
Creating SSH2 DSA key; this may take soting SSH2 ECDSA key; this may take some time ...
ssh start/running, process 3144
Setting up ssh-import-id (2.10-0ubuntu1) ...
UBUNTU >

Then I was able to connect as follows:

UBUNTU > ssh localhost
The authenticity of host 'localhost (127.0.0.1)' can't be established.
ECDSA key fingerprint is 56:30:a1:d5:23:9b:3f:a4:3b:30:6c:2c:07:c5:8e:3e.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'localhost' (ECDSA) to the list of known hosts.
andrew@localhost's password:
Welcome to Ubuntu 12.04 LTS (GNU/Linux 3.2.0-23-generic-pae i686)

 * Documentation:  https://help.ubuntu.com/

The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.

No mail.
UBUNTU >

/etc/services

The /etc/services file specifies which port a program must use when it connects to a UNIX or Linux machine. I tested this example using UBUNTU on my stand-alone PC so the connections are made to localhost. According to /etc/services, you must connect via port 21 if you wish to use ftp: 

UBUNTU > cat /etc/services|grep ftp

ftp-data        20/tcp
ftp             21/tcp
tftp            69/udp
sftp            115/tcp
ftps-data       989/tcp             # FTP over SSL (data)
ftps            990/tcp
venus-se        2431/udp            # udp sftp side effect
codasrv-se      2433/udp            # udp sftp side effect
gsiftp          2811/tcp
gsiftp          2811/udp
frox            2121/tcp            # frox: caching ftp proxy
zope-ftp        8021/tcp            # zope management by ftp

UBUNTU > ftp localhost 21
Connected to localhost.
220 (vsFTPd 2.3.5)
Name (localhost:andrew):
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> pwd
257 "/home/andrew"
ftp>

… but if you try using a different port, you are rejected:

 

UBUNTU > ftp localhost 42
ftp: connect: Connection refused
ftp>

The UNIX and Linux banner Command

With the banner command, you can use the # symbol to create large messages:

UBUNTU > banner Andrew
   #
  # #    #    #  #####   #####   ######  #    #
 #   #   ##   #  #    #  #    #  #       #    #
#     #  # #  #  #    #  #    #  #####   #    #
#######  #  # #  #    #  #####   #       # ## #
#     #  #   ##  #    #  #   #   #       ##  ##
#     #  #    #  #####   #    #  ######  #    #

UBUNTU > 

If the message has two words, the second appears below the first:

UBUNTU > banner Red Rum
######
#     #  ######  #####
#     #  #       #    #
######   #####   #    #
#   #    #       #    #
#    #   #       #    #
#     #  ######  #####

######
#     #  #    #  #    #
#     #  #    #  ##  ##
######   #    #  # ## #
#   #    #    #  #    #
#    #   #    #  #    #
#     #   ####   #    #

UBUNTU >

But, if you put the message in quotes, the two words appear on the same line:

UBUNTU > banner 'Red Rum'
######                          ######
#     #  ######  #####          #     #  #    #  #    #
#     #  #       #    #         #     #  #    #  ##  ##
######   #####   #    #         ######   #    #  # ## #
#   #    #       #    #         #   #    #    #  #    #
#    #   #       #    #         #    #   #    #  #    #
#     #  ######  #####          #     #   ####   #    #

UBUNTU >

chown

You can change the owner of a file with the chown command. Here is a file:

UBUNTU > ls -l
total 0
-rw-rw-r-- 1 andrew users 0 Aug 22 22:09 file1
UBUNTU >

The file is owned by andrew. If you want to change the owner to fred, you can do so as follows:

UBUNTU > sudo chown fred file1
UBUNTU > ls -l
total 0
-rw-rw-r-- 1 fred users 0 Aug 22 22:09 file1
UBUNTU >

How to Create a File of a Particular Size in UNIX or Linux

I needed a file with a size of 512 bytes for an Oracle test. I created it as follows:

UBUNTU > dd if=/dev/zero of=test1 bs=1 count=512
512+0 records in
512+0 records out
512 bytes (512 B) copied, 0.0140867 s, 36.3 kB/s
UBUNTU > ls -l test1
-rw-rw-r-- 1 andrew andrew 512 Aug 11 22:34 test1
UBUNTU >

To create a file with a size of 1000 bytes, you only have to change count=512 to count=1000:

UBUNTU > dd if=/dev/zero of=test2 bs=1 count=1000
1000+0 records in
1000+0 records out
1000 bytes (1.0 kB) copied, 0.0174102 s, 57.4 kB/s
UBUNTU > ls -l test2
-rw-rw-r-- 1 andrew andrew 1000 Aug 11 22:35 test2
UBUNTU >

UBUNTU Block Size

You can see the block size in UBUNTU as follows: 

UBUNTU > sudo dumpe2fs -h /dev/sda5|grep -i "block size"

dumpe2fs 1.42 (29-Nov-2011)

Block size: 4096

UBUNTU >

Disk Speed

You can use the following command to see the speed of a hard disk: 

UBUNTU > time dd if=/dev/zero of=large_file \

> bs=4096 count=2000000

2000000+0 records in

2000000+0 records out

8192000000 bytes (8.2 GB) copied, 192.95 s, 42.5 MB/s

real 3m13.102s

user 0m6.148s

sys 1m29.718s

UBUNTU >

hostname and uname -n

You can see the name of the machine you are using with the hostname command:

Linux > hostname
LUBUNTU-Laptop
Linux >

The uname -n command does the same thing:

Linux > uname -n
LUBUNTU-Laptop
Linux >