Linux Commands - Basic commands for Beginners

Linux Commands - Basic commands for Beginners

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  * 1 Linux BasicCommands
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  * 2 Operating SystemConcept • An operating system (OS) is a resource manager • It is a set of software routines: – that allow users and application programs to access system resources – in a safe, efficient and abstract way – CPU, memory, disks, modems, printers network cards etc. • A general operating system architecture can be understood by the figure Users Shell or GUI Application Programs System Utilities System Call Library Operating System Kernel Dual Processor with 2 GB RAM, 160 GB Hard Disk
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  * 3 Operating SystemConcept • The kernel controls the hardware • It provides functions like – Handling of interrupts from the devices – Allocation of memory to programs – Sharing of CPU among the programs • Basic kernel services are exposed to higher-level programs through a library of system calls • Application Programs and System Utility Programs make use of system calls – Launched using a shell/GUI • The OS may differ from one another on the basis of: – System calls – System utilities – User interface they provide – Resource scheduling policies implemented by the kernel
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  * 4 A LinuxDistribution • A distribution comprises of: – Kernel • 2.6.9-89.0.11.EL.cernsmp – System Utilities • File copy, hard disk repair/defragment etc. – GUI • GNOME, KDE – Application Programs • Open office, evolution, firefox, gedit, gftp. konqueror, evince, kdevelop, kview, emace, vim etc.
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  * 5 Typical DirectoryStructure • Linux Filesystem is laid out in a hierarchical tree structure. • Top level directory is called root “/”
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  * 7 Summary: DirectoryStructure • Home Directories: /root,/home/username • User Executables: /bin, /usr/bin, /usr/local/bin • System Executables: /sbin, /usr/sbin, /usr/local/sbin • Other Mountpoints: /media, /mnt • Configuration: /etc • Temporary Files: /tmp • Kernels and Bootloader: /boot • Server Data: /var, /srv • System Information: /proc, /sys • Shared Libraries: /lib, /usr/lib, /usr/local/lib
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  * 8 Logging intoa Linux System • Two types of login screens – virtual consoles (text-based) – graphical logins (display managers) • Login using login name and password • Each user has a home directory for personal file storage
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  * 9 Absolute &Relative Paths • Absolute pathnames – Begin with a forward slash – Complete "road map" to file location – Can be used anytime you wish to specify a file name • Relative pathnames – Do not begin with a slash – Specify location relative to your current working directory – Can be used as a shorter way to specify a file name
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  * 10 Basic LinuxCommands • ls, listing files and directories – ls –a – ls –l – ls -la • clear, clears the screen • echo, display a line or text – echo “any text”, echo $HOSTNAME • exit, exit the current session/shell • file, determine file type – file <file name/path>
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  * 11 Basic LinuxCommands • cd, change directory – cd .. – cd – – cd ~/mydir – cd /home/usman – cd • su, switch user, su – (complete user environment) • id, print user and group ids • passwd, change password – yppasswd
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  * 12 Basic LinuxCommands • man, manual pages – man <command> • info, information pages – info <command> • command --help, basic help by author – ls --help, man --help • pwd, present working directory
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  * 13 Basic LinuxCommands • cp, copy files and directories – cp [options] file destination • More than one file may be copied at a time if the destination is a directory: – cp [options] file1 file2 destination • If the destination is a directory, the copy is placed there • If the destination is a file, the copy overwrites the destination • If the destination does not exist, the copy is renamed
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  * 14 Basic LinuxCommands • mv, move and/or rename files and directories – mv [options] file destination • More than one file may be moved at a time if the destination is a directory: – mv [options] file1 file2 destination • In mv also, the destination works like cp • mkdir, creates directories – mkdir <directory name/path> • rmdir, removes empty directories – rmdir < directory name/path>
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  * 15 Basic LinuxCommands • touch, create empty files or update file timestamps – touch <file name/path> • rm, remove files – rm [options] <file name/path> – rm -i file (interactive) – rm -r directory (recursive) – rm -f file (force) • rm –r, recursively removes directory trees – rm –rf <directory name/path>
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  * 16 Basic LinuxCommands • whoami, print user id • locate, finds files using a pre-built database. • find, Finds files and directories in real-time. – locate is faster but relies on an updated index; find is slower but always accurate. • whereis, Shows locations of executables, source code, and manual pages
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  * 17 File Permissionsin Linux
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  * 18 File Permissionsin Linux Octal Binary Permissions 0 000 _ _ _ 1 001 _ _ x 2 010 _ w _ 3 011 _ w x 4 100 r _ _ 5 101 r _ x 6 110 r w _ 7 111 r w x
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  * 19 Basic LinuxCommands • chmod, changing permissions of files/directories – Octal mode • chmod 644 <file name/path> • chmod 755 <file name/path> • chmod 6 <file name/path> – Symbolic mode • chmod u+x, g-r, o+x <file name/path> • chmod a+x <file name/path> • chmod =x <file name/path>
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  * 20 Shell ScriptingBasics #!/bin/sh echo "Welcome to Linux -- $USER" echo "Today is: $(date)" echo "You are working in: $(pwd)" echo "Enter your last name:" read LNAME echo "Hello -- $LNAME" echo "Enter the first number:" read X echo "Enter the second number:" read Y PRODUCT=$((X * Y)) echo "The product is: $PRODUCT" echo "Bye Bye..."
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