Chapter 9 Part II Linux Command Line

Access to Linux• Authenticated login using a Linux account is required to

access a Linux system. The Linux prompt will be shown only if the authentication information is correct.

• The Linux prompt includes the user name, followed by a @machine name. ( wpilkey@Linux:~# )

• The Linux command syntax is very basic, and starts with a Linux command separated by spaces, and followed by optional parameters and switches.– A switch changes the way a command runs.

Basic Linux Skills and Concepts

• Comparing DOS and Linux – DOS is single user, single tasking– Linux is multi-user, multitasking– Many differences & Similarities in command-line interface

• The Shell– Character-mode user interface component– Processes commands– Issues error messages and other feedback – Called COMMAND.COM in DOS– Called BASH in Linux

• Case Sensitivity– DOS is case insensitive– Linux is case sensitive– Designation of Switches – A switch changes the way a command runs– Switches in DOS begin with a slash (/)– Switches in Linux begin with a dash (-)

• Use of Spaces– DOS allows a space to be omitted between a command and a switch– Each part of a Linux command must be separated by a space – These commands will not work in Linux

– shutdown-h now – shutdown -hnow

Basic Linux Skills and Concepts

• Paths– DOS and Windows

• Paths begin with a drive designator (C:)• A backslash (\) after the drive designator indicates the

root of that logical drive• Portions of path separated with backslashes

– Linux• No drive letter designation• Path begins with a slash (/) indicating the root• Portions of path separated with slashes• Example: /etc/gtk• Everything (devices, services, etc.) is a file

– /dev/sda0 (the first hard drive on a SCSI interface)– /dev/hda1 (the first hard drive on an IDE interface)

Basic Linux Skills and Concepts

• Linux Feedback– DOS and Linux similar in providing cryptic feedback– No feedback when command is successful– Both provide error messages – Linux provides minimum output

• DOS dir command lists more information on files• Linux ls command (without switches) only shows file names

Basic Linux Skills and Concepts

• The Command Syntax– command<space>option<space>option…– Options preceded by a - hyphen are switches– Multiple switches can be combined behind one hyphen– Another type of option is a parameter

• File name, directory, device name, or other.• Parameter at end of command

– Syntax: command –switch parameter– Example: ls –a /etc

Basic Linux Skills and Concepts

• Command-Line History – Shell commands are saved during a session– Scroll through the commands at the $ prompt

• Up Arrow and Down Arrow

– Move within a command to edit it• Left Arrow and Right Arrow

– Press Enter to run command– Command history saved in the bash_history file

• Command Completion– A feature that completes a command line – Enter portion of a command and press the Tab key– Linux will try to guess the remaining portion

Basic Linux Skills and Concepts

Shells, Terminals, and the Kernel

• Terminal– Channel that allows a certain user to log in and

communicate with the kernel via a user interface

Shells, Terminals, and the Kernel

• Shell– User interface that accepts input from the user and

passes the input to the kernel for processing– Shell used by default in Linux is the BASH Shell

The Linux Directory Structure• Is arranged hierarchically using a series of directories to

store files, and the location of these directories and files can be described using absolute or relative pathnames

Figure 4-2: The Linux filesystem structure

Linux

Windows

DOS versus Linux • Case sensitivity – Linux is case-sensitive, DOS is Not.

• Switches – Linux switches start with a hyphen (-) while DOS switches start with a slash (/).

• Spaces – Linux command line must be separated by a space. DOS commands can work with or without a space

• Path - Linux uses the forward slash (/) to indicate a path to a folder, while DOS uses the backslash (\) character to indicate a path to a folder.

• Output – Linux provides only the minimum output while DOS provides a very descriptive output.

Shell Metacharacters• Metacharacters: characters that help define other characters • Key combinations that have special meaning in the Linux

Command Sampler

Command Line

• The pwd command Print Working Directory - The default action is to show the current folder as an absolute path.

• The cd command Change Directory - change the current working directory to a specific Folder.

# cd /usr/local/sybase move to sybase folder

# pwd print current folder

/usr/local/sybase

# cd .. move up one folder

# pwd print current folder

/usr/local/

File Permissions

Anatomy of ls –l output

Listing the Contents of a Folder • The ls command is used to list the contents of a folder and

information about files, by default the current directory.• By default, the ls command only provides the names of

visible files in the current folder.• Some frequently used swicthes: -l, -a, -F

# ls –al

total 109drwxr-xr-x 18 root root 4096 Jun 9 21:12 ./drwxr-xr-x 18 root root 4096 Jun 9 21:12 ../drwxr-xr-x 2 root root 4096 Jun 9 21:14 bin/drwxr-xr-x 3 root root 1024 Jun 9 20:32 boot/drwxr-xr-x 6 root root 36864 Jul 12 10:26 dev/drwxr-xr-x 34 root root 4096 Jul 12 10:25 etc/drwxr-xr-x 5 root root 4096 Jun 9 21:28 home/

File type, permissions, hard link count, file owner, group owner, size, mod date, directory name, filename or pointer.

Creating folders and Deleting in Linux

• The mkdir command Create new folder(s), if they do not already exist.

Create labdir directory underneath the current directory

# mkdir labdir

• The rmdir command Remove folder(s), if they are empty.

# rmdir labdir

• The ‘rm’ command is used for deleting files & folders• The command requires at least one parameter – the name

of the file to be deleted. Defaults to –i or interactive prompt

# rm filename

Renaming or Moving Files in Linux• The mv command is used to rename a file or to move a

file from one folder to another. Defaults to –i or interactive prompt

• The command required two parameters – the name of the original file and the new name or location of the file.

Rename hosts file to hosts2, if hosts2 exists, you are prompted

# mv hosts hosts2

Force rename without prompting# mv –f hosts hosts2

Copying Files in Linux • The cp command is used to copy one or more files to

another location. Can be used to do backups. Defaults to –i or interactive prompt

• The command requires two parameters – the source file and the destination where the file has to be copied.

Copy SOURCE to DEST, or multiple SOURCE(s) to DIRECTORY

copy home directory to floppy-f switch means remove existing destinations, never prompt # cp -f /mnt/floppy/* /home/simon

Copy file hosts from directory /etc to this directory “ .”# cp /etc/hosts .

Displaying the Contents of a File • The cat command displays the entire contents of a file.# cat filename

• The more and less commands display the contents of a file one page at a time, ironically less provides more emulation and extensive enhancements, (moving, jumping, searching, line edit)

• The head command displays the first ten lines of a file.

• The tail command displays the last ten lines of a file.

Logoff and Shutdown in Linux • The exit command or the CTRL-D key combination can be used to log out Linux

• The shutdown –h now command is used to shut down the Linux machine immediately, and halt after shutting down. Normally root can shut down Linux from command line– A Linux GUI will allow ordinary user to shutdown Select Log Out |

Shutdown– Root can enable/disable this feature in the GUI– shutdown –h now

• Linux shuts down and turns off the computer– shutdown –r now

• Linux shuts down and reboots the computer

Basic Linux Skills and Concepts

• The Help Manual– Online manual accessed with man command– Syntax: man command

• Where command is the name of the command you wish to view

• Enter man man to see documentation for the man • Page Down & Page Up to scroll one screen at a time• Up Arrow and Down Arrow to scroll one line at a time

– man shutdown• The man command will display the complete

list of switches for the shutdown command

The Filesystem Hierarchy Standard (FHS)

Table 5-1: Linux directories defined by FHS