Unix/Linux Fundamentals

Setting the PATH

When you type any command on command prompt, the shell has to locate the command before

it can be executed.

The PATH variable specifies the locations in which the shell should look for commands. Usually it

is set as follows-

[oracle@localhost ~]$ PATH=/bin:/usr/bin

[oracle@localhost ~]$

Process in Unix

# Forground Process - Every process that you start runs in the foreground. It gets its input from the

keyboard and sends its output to the screen.

# Background Processes - A background process runs without being connected to your keyboard. If the background process requires any keyboard input, it waits. The simplest way to start a background process is to add an ampersand ( &) at the end of the command. The advantage of running a process in the background is that you can run other commands also. We do not have to wait until it completes to start another.

Listing Running Processes(ps)

It is easy to see your own processes by running the ps (process status) command. It can be used with the –f option for more information. It is used as follows –

[oracle@localhost ~]$ ps

  PID TTY          TIME CMD

 7214 pts/1    00:00:00 bash

[oracle@localhost ~]$ ps -f

UID        PID  PPID  C STIME TTY          TIME CMD

oracle    7214  7212  0 19:51 pts/1    00:00:00 bash

Stopping Processes

Ending a process can be done in several different ways. Often, from a console-based command,

sending a CTRL + C keystroke (the default interrupt character) will exit the command. This

works when process is running in foreground mode.

Kill Command(kill)

If a process is running in background mode then first you would need to get its Job ID using ps

command and after that you can use kill command to kill the process as follows-

[oracle@localhost ~]$ ps -f

UID        PID  PPID  C STIME TTY          TIME CMD

oracle    7214  7212  0 19:51 pts/1    00:00:00 bash

[oracle@localhost ~]$ kill 7214

Here  kill  command would terminate first_one process. If a process ignores a regular kill command, you can use kill -9 followed by the process ID as follows-

[oracle@localhost ~]$ kill -9 7214

Ping Utility in Unix

The ping command sends an echo request to a host available on the network. Using this command you can check if your remote host is responding well or not. The ping command is useful for the following-

# Tracking and isolating hardware and software problems.

# Determining the status of the network and various foreign hosts.

# Testing, measuring, and managing networks.

Ping is done as follow-

$ping hostname or ip-address

File Transfer Protocol(ftp) Utility

Here ftp stands for File Transfer Protocol. This utility helps you to upload and download your file

from one computer to another computer. The ftp utility has its own set of UNIX like commands which allow you to perform tasks as follows-

# Connect and login to a remote host.

# Navigate directories.

# List directory contents

# Put and get files

# Transfer files as ascii, ebcdic or binary

The ftp command is used as follows-

$ftp hostname or ip-address