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| Getting started: | |
| ---------------- | |
| passwd : change user password | |
| whoami : know which user are you logged-in | |
| logout : logout from the system | |
| init 0 : powers off the system using predefined scripts to synchronize and clean up the system prior to shutdown | |
| reboot : reboot the system | |
| shutdown : shutdown the system | |
| .program name : invisible file is one whose first character is the dot or period character | |
| uname : display the operating system information | |
| date : display the date and time | |
| cal : display the calendar | |
| su - username : change to the directory to other user | |
| Moving around the file system: | |
| ------------------------------ | |
| pwd : show the "present working directory", or current directory | |
| cd : change current directory to your HOME directory | |
| cd / : change a working directory within hierarchy of filesystem | |
| cd .. : change current directory to the parent directory of the current directory | |
| cd ~ : change current directory to the home directory | |
| cd /etc/ : contains all system related configuration files | |
| cd /proc/ : used as an interface to kernel data structures | |
| sudo : allows a user with proper permissions to execute a command as super user | |
| sudo -s : used to do actions as super user | |
| command1;command2; : execute multiple commands | |
| ln -s : create a symbolic link file | |
| Listing directory contents: | |
| --------------------------- | |
| ls : list a directory | |
| ls -i : list your files including the inode numbers | |
| ls -a : list all files and directories including hidden files and directories | |
| ls -l : lists your files including the exact size of the file, who owns the file and the permissions, and when it was last modified | |
| ls -R : lists the content of a directory and all its subdirectories | |
| ls directory name : list the files in a directory | |
| Changing file permissions and attributes: | |
| ----------------------------------------- | |
| ls -l|grep keypair : check the permission of a keypair | |
| chown user filelist : stands for "change owner" and is used to change the owner of a file | |
| chgrp group filelist : stands for "change group" and is used to change the group of a file | |
| chmod a+rw filename : give read and write permissions on the file to all users | |
| chmod a-rw filename : take read and write permissions on the file to all users | |
| chmod 400 filename : changes the permissions of file for the owner, and for the group and the world | |
| umask 022 filename : affects and modifies the default file permissions assigned to the file or directory | |
| The options of chmod are as follows: | |
| ------------------------------------ | |
| Symbol Meaning | |
| u : user | |
| g : group | |
| o : other | |
| a : all | |
| r : read | |
| w : write (and delete) | |
| x : execute (and access directory) | |
| + : add permission | |
| - : take away permission | |
| Viewing and editing files: | |
| -------------------------- | |
| cat filename -b : see the content of a file and display line number by using the option -b | |
| cat /proc/cpuinfo : check CPU info | |
| cat /etc/issue.net : check OS info | |
| cat /proc/meminfo : check memory info | |
| fdisk -l : check the fixed disks in hard drive | |
| route -n : check default gateway | |
| touch filename : create a filename | |
| history : show ordered list of all the commands entered | |
| file * : classifies the named files according to the type of data they contain, for example ascii (text), pictures, compressed data, etc.. | |
| echo file/variable : display a line of text | |
| find filename : search for a filename in the system | |
| cmp file1 file2 : compare the contents of two files byte by byte | |
| comm file1 file2 : compare the contents of two sorted files line by line | |
| spell filename : check text for spelling error | |
| Archiving files: | |
| ---------------- | |
| compress filename : reduces the size of a file with format (.zip) | |
| uncompress filename : uncompress the file with format (.zip) | |
| gzip filename : zip the file and place it in a file format in smaller sizes (.gzip) | |
| gunzip filename.gz : unzip the file with format (.gzip) | |
| gzcat filename : displays files that were compressed with either the gzip or compress commands | |
| tar -cf filename : create a new archive file and specify the archive file | |
| zip trgtfile srcfiles : compresses and archives multiple files into a single file in one go | |
| zcat : display a compressed file | |
| Basics of the vi editor: | |
| ------------------------- | |
| vi : open the default editor mode | |
| vi filename : edit filename starting at line 1 | |
| vi -R filename : open an existing file in read only mode | |
| view filename : opens an existing file in read only mode | |
| K : moves the cursor up one line | |
| J : moves the cursor down one line | |
| H : moves the cursor to the left one character position | |
| L : moves the cursor to the right one character position | |
| Command mode in vi editor: | |
| -------------------------- | |
| :w<Return> : write current contents to file | |
| :w filename1<Return> : save the file as filename1 | |
| :q! : exit vi without saving any of the changes | |
| ZZ or :wq : exit vi with saving the changes in file | |
| <ESC> : terminate insertion or overwrite mode | |
| :f filename : renames current file to filename | |
| :w filename : write to file filename | |
| :e filename : opens another file with filename | |
| :cd dirname : changes current working directory to dirname | |
| U : restore the current line to the state it was in before the cursor entered the line | |
| U : undo the last change to the file. Typing 'u' again will re-do the change | |
| :! ls : check whether a file exists before you try to save your file to that filename | |
| :w >> filename : append the contents of a file to another file | |
| :set nu : show line numbers | |
| :set nonu : hold line numbers | |
| Moving within a vi file: | |
| ------------------------ | |
| 0 or | : positions cursor at beginning of line | |
| $ : positions cursor at end of line | |
| w : positions cursor to the next word | |
| b : positions cursor to previous word | |
| ( : positions cursor to beginning of current sentence | |
| ) : positions cursor to beginning of next sentence | |
| E : move to the end of Blank delimited word | |
| { : move a paragraph back | |
| } : move a paragraph forward | |
| [[ : move a section back | |
| ]] : move a section forward | |
| n| : moves to the column n in the current line | |
| 1G : move to the first line of the file | |
| G : move to the last line of the file | |
| nG : move to nth line of the file | |
| :n : move to nth line of the file | |
| H : move to top of screen | |
| nH : moves to nth line from the top of the screen | |
| M : move to middle of screen | |
| L : move to botton of screen | |
| nL : moves to nth line from the bottom of the screen | |
| :x : colon followed by a number would position the cursor on line number represented by x | |
| Editing in a vi file: | |
| --------------------- | |
| i : inserts text before current cursor location | |
| I : inserts text at beginning of current line | |
| a : inserts text after current cursor location | |
| A : inserts text at end of current line | |
| o : creates a new line for text entry below cursor location | |
| O : creates a new line for text entry above cursor location | |
| Deleting in a vi file: | |
| ---------------------- | |
| x : deletes the character under the cursor location | |
| X : deletes the character before the cursor location | |
| dw : deletes from the current cursor location to the next word | |
| d^ : deletes from current cursor position to the beginning of the line | |
| d$ : deletes from current cursor position to the end of the line | |
| D : deletes from the cursor position to the end of the current line | |
| Changes in a vi file: | |
| -------------------- | |
| cc : removes contents of the line, leaving you in insert mode | |
| cw : changes the word the cursor is on from the cursor to the lowercase w end of the word | |
| r : replaces the character under the cursor, vi returns to command mode after the replacement is entered | |
| R : overwrites multiple characters beginning with the character currently under the cursor. You must use Esc to stop the overwriting. | |
| s : replaces the current character with the character you type. Afterward, you are left in insert mode | |
| S : deletes the line the cursor is on and replaces with new text. After the new text is entered, vi remains in insert mode | |
| nP : recover a recent deletion where n is up to 3 characters | |
| Copy and paste in a vi file: | |
| ---------------------------- | |
| Yy : copies the current line | |
| Yw : copies the current word from the character the lowercase w cursor is on until the end of the word | |
| P : puts the copied text after the cursor | |
| P : puts the yanked text before the cursor | |
| Search in a vi file: | |
| -------------------- | |
| /word : searches forwards (downwards) in the file for word | |
| ?word : searches backwards (upwards) in the file for word | |
| fc : move forward to c | |
| Fc : move back to c | |
| :s/search/replace/g : search for the word 'search' and replace the word with 'replace' | |
| n : searches for the next occurrence of the string after searching command for a string | |
| N : searches for the previous occurrence of the string after searching command for a string | |
| Basics of the nano editor: | |
| -------------------------- | |
| nano filename : opens a new text file in nano editor | |
| Ctrl + O : saves a file, 'O' stands for output | |
| Ctrl + X : exits the nano program, 'X' stands for exit | |
| Ctrl + G : opens a help menu | |
| nano ~/.bash_profile : opens a file used to store environment settings | |
| source ~/.bash_profile : activates the changes in a file for the current session | |
| alias var="command" : allows you to create keyboard shortcuts, or aliases, for commonly used commands | |
| export USER="var" : makes the variable to be available to all child sessions initiated from the session you are in to persist across programs | |
| Moving, renaming, and copying files: | |
| ------------------------------------ | |
| . : means current directory | |
| cp srcfile destfile : copy a directory/file from source to destination or the content of a directory/file from source to destination | |
| cp . : copy a file to the current directory | |
| cp -r srcdir destdir : copy a directory from source to destination | |
| mv file1 newname : rename a file | |
| mv file1 ~/AAA/ : move file1 into sub-directory AAA in your home directory | |
| mkdir directory name : make a new directory | |
| mkdir dir1 dir2 : make directories (dir1 and dir2) | |
| mkdir /dir/sub-dir : creates the directory sub-dir in the directory | |
| rmdir dir1 dir2 : remove an empty directory | |
| Displaying the contents of a file on the screen: | |
| ------------------------------------------------ | |
| clear : clear all text and leave you with the % prompt at the top of the window | |
| less filename : writes the contents of a file onto the screen a page at a time | |
| head filename : writes the first ten lines of a file to the screen | |
| tail filename : writes the last ten lines of a file to the screen | |
| more filename : display data in paginated form | |
| [space-bar] : if you want to see another page | |
| [q] : if you want to quit reading | |
| Searching the contents of a file: | |
| --------------------------------- | |
| less filename/[word] : search for a word after using the command less | |
| grep science filename : searches files for specified words (e.g. science) or patterns | |
| grep -i word filename : -i used to ignore upper/lower case distinctions | |
| grep -i 'pattern' file : used to search for a phrase or pattern, you must enclose it in single quotes | |
| grep -R directory : search within a directory | |
| wc -w filename : count words in the file | |
| wc -l filename : count letters in the file | |
| sed 's/find/replace/' : search the file for the first instance of the word "find" and replaces it with "replace" | |
| sed 's/find/replace/g' : search the file for the word "find" and replaces it with "replace" globaly | |
| Redirecting the output: | |
| ----------------------- | |
| > : redirect the output of a command | |
| >> : appends (adds) the output (content) to the file on the right | |
| cat > list : create a file called list then type any values for the file | |
| Ctrl D : used to stop the command | |
| Redirecting the input: | |
| ---------------------- | |
| < : redirect the input of a user | |
| sort < filename : used to alphabetically or numerically sorts a list | |
| sort -n filename : used to sort numerically a list | |
| sort -f filename : used to sort upper and lower-case together | |
| sort -r filename : used to reverse the order of sort | |
| Pipes: | |
| ------ | |
| who : used to see who is on the system with you | |
| who | sort : used to see who is on the system with sorted users | |
| cat filename | uniq : filters out adjacent, duplicate lines in a file | |
| command1 | command2 : pipe the output of command1 to the input of command2 often referred to as filter | |
| Wildcards: | |
| ---------- | |
| ls list* : list all files in the current directory starting with list | |
| ls *list : list all files in the current directory ending with list | |
| ls ?list : list all files that have one character starting with list | |
| Getting help: | |
| ------------- | |
| man command : read the online manual page for a command, which options a particular command can take, and how each option modifies the behaviour of the command | |
| apropos keyword : match commands with keyword in their man pages when you are not sure of the exact name of a command | |
| Processes and Jobs: | |
| ------------------- | |
| jobs : list current jobs | |
| kill %number of job : kill job number | |
| ps : list current processes | |
| sleep seconds : waits a given number of seconds before continuing | |
| Running the software: | |
| --------------------- | |
| bin : The binary executables needed to run a program | |
| info : GNU info formatted documentation | |
| man : Man pages | |
| share : Shared data files | |
| ./program name : Run the program name in the current directory | |
| Environment Variables: | |
| ---------------------- | |
| USER : your login name | |
| HOME : the path name of your home directory | |
| HOST : the name of the computer you are using | |
| ARCH : the architecture of the computers processor | |
| DISPLAY : the name of the computer screen to display X windows | |
| PRINTER : the default printer to send print jobs | |
| PATH : the directories the shell should search to find a command | |
| VARIABLE_NAME=value : set a variable name and assign it to 'value' without using the $ sign | |
| $VARIABLE_NAME : access the variable name with the $ sign | |
| PS1 : defines the makeup and style of the command prompt | |
| env : returns a list of the environment variables for the current user | |
| Printing Files: | |
| --------------- | |
| nroff filename : formats documents for display or line-printer | |
| pr -NUM filename : format file on screen to produce NUM-number of columns | |
| lp/lpr -nNUM filename : print file with NUM-number of copies | |
| lpstat/lpq -o : shows what's in the printer queue | |
| cancel printername : terminates a printing request from the lp command | |
| lprm printername : terminates lpr requests | |
| Background Processes: | |
| --------------------- | |
| command & : execute the command in a background process | |
| ps -f : reports a snapshot of the status of currently running processes | |
| top : updates frequently and shows information about physical and virtual memory, CPU usage, load averages, and your busy processes | |
| nohup command [arg] : runs a command, making it immune to any HUP (hangup) signals (e.g. nohup ./file.sh &) | |
| Networking commands: | |
| -------------------- | |
| curl URL : open the url | |
| wget URL : download file over a network | |
| apt-get [install] : used to install packages on your system | |
| yum : perform system updates, installation of new packages, removal of old packages and perform queries on the installed and/or available packages | |
| ssh -i keypair root@IP : allows you to connect and log in to a specified host | |
| scp [user@host1:]file [[user@]host2:]file2 : copies files securely between hosts on a network | |
| scp srcfile user@host:directory/trgtfile : copy a file from local directory to a remote host | |
| scp user@host:/directory/srcfile trgtfile : copy a file from remote host to a local directory | |
| mail [-s subject] [-c cc-addr] [-b bcc-addr] to-addr : send mail to the specified address | |
| Unix Communication: | |
| ------------------- | |
| ping URL/IP : used to test whether another system is reachable over a network | |
| ftp host : used to to transfer files to and from a remote network site | |
| ftp>open : opens a connection with another computer on the network | |
| ftp>put filename : upload filename from local machine to remote machine | |
| ftp>get filename : download filename from remote machine to local machine | |
| ftp>mput file list : upload more than one files from local machine to remove machine | |
| ftp>mget file list : download more than one files from remote machine to local machine | |
| ftp>prompt off : turns prompt off, by default you would be prompted to upload or download movies using mput or mget commands | |
| ftp>prompt on : turns prompt on | |
| ftp>Dir : list all the files available in the current directory of remote machine | |
| ftp>cd dirname : change directory to dirname on remote machine | |
| ftp>lcd dirname : change directory to dirname on local machine | |
| ftp>Quit : logout from the current login | |
| telnet host : allows a computer user at one site to make a connection, login and then conduct work on a computer at another site | |
| finger host/user : displays information about users on a given host either local, remote or specifying a certain user | |
| Unix Shell: | |
| ----------- | |
| #!/bin/sh : alert the system that a shell script is being started | |
| # comment : put comments in a script | |
| ./file.sh : execute the shell script | |
| var_name=var_value : define variables | |
| $var_name : access variable value | |
| readonly variable_name : mark variables as read-only and its value cannot be changed | |
| unset variable_name : tells the shell to remove the variable from the list of variables that it tracks | |
| File System: | |
| ------------ | |
| / : the root directory which should contain only the directories needed at the top level of the file structure | |
| /bin : where the executable files are located. They are available to all user | |
| /dev : device drivers. | |
| /etc : supervisor directory commands, configuration files, disk configuration files, valid user lists, groups, ethernet, hosts | |
| /lib : contains shared library files and sometimes other kernel-related files | |
| /boot : contains files for booting the system | |
| /home : contains the home directory for users and other accounts | |
| /mnt : used to mount other temporary file systems, such as cdrom and floppy for the CD-ROM drive and floppy diskette drive, respectively | |
| /proc : contains all processes marked as a file by process number or other information that is dynamic to the system | |
| /tmp : holds temporary files used between system boots | |
| /usr : includes administrative commands, shared files, library files, and others | |
| /var : contains variable-length files such as log and any other type of file that may contain a variable amount of data | |
| /sbin : contains binary (executable) files, usually for system administration. For examplefdisk and ifconfig utlities | |
| /kernel : contains kernel files | |
| file filename : identifies the file type (binary, text, etc) | |
| whereis filename : shows the location of a file | |
| which filename : shows the location of a file if it is in your PATH | |
| df -h : reports on the space left on the file system | |
| du : outputs the number of kilobyes used by each subdirectory | |
| mkfs.ext3 /dev/sdb : create file system and a parition and format it | |
| mount /dev/sdb /mnt : mounts a file system to be ready to be used to the /mnt directory | |
| unmount /dev/sdb /mnt : unmount (remove) the file system from the mount point | |
| quota : displays disk usage and limits for a user of group | |
| edquota : this is a quota editor. Users or Groups quota can be edited using this command | |
| quotacheck : scan a filesystem for disk usage, create, check and repair quota files | |
| User Administration: | |
| -------------------- | |
| useradd user_name : adds accounts to the system | |
| -d homedir : specifies home directory for the account | |
| -g groupname : specifies a group account for this account | |
| -m : creates the home directory if it doesn't exist | |
| -s shell : specifies the default shell for this account | |
| -u userid : specify a user id for this account | |
| usermod user_name : modifies account attributes | |
| userdel user_name : deletes accounts from the system | |
| groupadd group_name : adds groups to the system | |
| groupmod group_name : modifies group attributes | |
| groupdel group_name : removes groups from the system | |
| Bash Scripting: | |
| --------------- | |
| [ $e -gt 2 ] : compare value of e if it's greater than 2 and evaluate the output as an error code | |
| echo $? : print last error code in the terminal | |
| [[ $e -gt 2 ]] : construct over the single bracket version and handle null-value variables |
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