Basic Linux Commands
Basic stuff |
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| cat filename.txt | Print the contents of filename.txt to your screen |
| cd - | Change to the last visited directory |
| cd .. | Cahnge one directory up |
| cd dirname | Change into directory "dirname" |
| cd ~ or cd | Change into your home directory |
| chmod | Changes file access permissions: USER - GROUP - EVERONE
0 = --- No permission |
| chmod 000 filename | No one can access |
| chmod 644 filename | Usually for text files |
| chmod 755 filename | Usually for executable scripts/files |
| chown root myfile.txt | Changes the owner of the file to root [requires root privileges]. |
| chown owner:group myfile.txt | Changes the owner and group of the file to new owner and "group" group [requires root privileges]. |
| cp -a /etc/* /root/etc/ | Copies all files, retaining permissions form one directory to another. |
| cp -av * /path/to/newdirectory | Copies all files and directories recurrsively in the current directory into newdirectory |
| cp filename filename.bak | Copies filename to filename.bak |
| file * | Prints out a list of all files/directories in a directory |
| file | Attempts to guess what type of file a file is by looking at it's content. |
| find / -name "filename" | Finds the file called "filename" on your filesystem starting the search from the root directory "/". |
| find | Utility to find files / directories on a computer. |
| grep | Looks for patterns in file(s) |
| grep word filename.txt | Shows all matches of word "word" in file filename.txt |
| grep -v word filename.txt | Shows all lines that do not match root |
| gv | View Postscript/PDF files |
| less | Similar to more command |
| ln -s /home/user/file1 /home/user/file2 | Now you can edit /etc/httpd.conf rather than the original. changes will affect the orginal, however you can delete the link and it will not delete the original. |
| ln | Create's "links" between files and directories |
| locate filename | Finds the file name and path of which contains the string "filename". Run 'updatedb' to build index. |
| ls -la | Shows all files (including ones that start with a period), directories, and details attributes for each file. |
| ls | List files in current directory. |
| more filename | Print content of file "filename" screen by screen. Use space bar to procceed to the next page, q is to quit. |
| mv | Move a file command |
| mv oldfilename newfilename | Move a file or directory from oldfilename to newfilename |
| nl | Number lines |
| od | View binary files and data |
| rm -f filename.txt | Deletes filename.txt, will not ask for confirmation before deleting. |
| rm -rf tmp/ | Recursively deletes the directory tmp, and all files in it, including subdirectories. |
| rm | Deletes a file |
| rm -i filename.txt | Will ask if you really want to delete it |
| stat | Display file attributes |
| tail -100 filename | Print the last 100 lines of the file to the screen |
| tail -f filename | Watch the file continuously, while it's being updated |
| tail filename | See the last 20 (by default) lines of filename |
| touch | Create an empty file |
| touch /home/user/filename.txt | Creates an empty file "filename.txt" in the directory /home/user/ |
| wc -l filename.txt | Counts # of lines in filename.txt |
| wc | Counts # of words |
| xdvi | View TeX DVI files |
| xxd | Also view binary files and data |
Editors |
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| pico, vi, emacs | The most popular editors |
| vi filename.txt | Edit filename.txt. All commands in vi are preceded by pressing the escape key.
Each time a different command is to be entered, the escape key needs to be used.
Except where indicated, vi is case sensitive.
H --- Upper left corner (home) :q! --- This force quits the file without saving and exits vi See quick reference quide in txt form. |
| emacs -nw filename.txt | C-\ t --- Tutorial suggested for new emacs users. C-x C-c exit emacs C-x C-f --- read a file into emacs C-f --- move forward one character |
Network commands |
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| arp | Command mostly used for checking existing Ethernet connectivity and IP address |
| ifconfig -a | Display into on all network interfaces on server, active or inactive.. |
| ifconfig | Display info on the network interfaces. |
| netstat -an | Shows all connections to the server, the source and destination ips and ports. |
| netstat -an |grep :80 |wc -l | Show how many active connections there are to apache (httpd runs on port 80) |
| netstat -rn | Shows routing table for all ips bound to the server. |
| netstat | Shows all current network connections. |
| nslookup beowulf.rutgers.edu | Query your default domain name server (DNS) for an Internet name (or IP number) host_to_find. |
| ping beowulf.rutgers.edu | Sends test packets to a specified server (beowulf.rutgers.edu in this example) to check if it is responding properly |
| route -n | Shows routing table for all ips bound to the server. |
| tcpdump | Print all the network traffic going through the network [requires root privileges].. |
| top -u root | Show processes running by user root only. |
| top | Shows live system processes in a formatted table, memory information, uptime and other useful info. While in top, Shift + M to sort by memory usage or Shift + P to sort by CPU usage |
| traceroute beowulf.rutgers.edu | Have a look how you messages travel to yahoo.com |
| w | Shows who is currently logged in and where they are logged in from. |
| who | This also shows who is on the server in an shell. |
System commands |
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| date | Print or change the operating system date and time |
| dmesg | less | Print kernel messages. |
| du -sh | Shows a summary of total disk space used in the current directory, including subdirectories. |
| du dirname -bh | more | Print detailed disk usage for each subdirectory starting at the "dirname". |
| du | Shows disk usage. |
| free | Memory info (in kilobytes). |
| fsck | Check a disk for errors [requires root privileges]. |
| hostname | Print the name of the local host. Use netconf (as root) to change the name of the machine. |
| kill -9 PID | Immediately kill process ID. |
| kill | Terminates a system process. |
| killall | program_name Kill program(s) by name. For example to kill instances of httpd, do 'killall bash'. |
| last -10 -a | Shows last 10 logins, with the hostname in the last field. |
| last -10 | Shows only the last 10 logins. |
| last | Shows who logged in and when. |
| lsmod | Show the kernel modules currently loaded [requires root privileges]. |
| man | topic Display the contents of the system manual pages (help) on the topic. Do 'man netstat' to find all details of netstat command including options and examples. |
| mount -t auto /dev/cdrom /mnt/cdrom | Mount the CD. The directory /mnt/cdrom must exist [often requires root privileges]. |
| mount -t auto /dev/fd0 /mnt/floppy | Mount the floppy. The directory /mnt/floppy must exist [often requires root privileges]. |
| mount | Mount local drive or remote file system [requires root privileges]. |
| ps U username | Shows processes for a certain user. |
| ps auxf | Shows all system processes like the above but organizes in a hierarchy that's very useful. |
| ps aux | Shows all system processes. |
| ps | ps is short for process status, which is similar to the top command. It's used to show currently running processes and their PID. A process ID is a unique number that identifies a process, with that you can kill or terminate a running program on your server (see kill command). |
| pwd | Print working directory, i.e., display the name of my current directory on the screen. |
| reboot | Reboot the machine [requires root privileges]. |
| sudo | The super-user do command that allows you to run specific commands that require root access. |
| time | Determine the amount of time that it takes for a process to complete. |
| uname -a | Displays info on about your server such as kernel version. |
| uptime | Show the number days server has been up including system load averages. |
| whoami | Print login name. |
Compression commands |
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| bzip2 | Compress files in bzip2 format |
| compress | Compress files. Compress filename end with .Z |
| gzip filename | Compresses file with name filename and produces file with name filename.gz |
| gzip -d filename.gz | Uncompresses file filename.gz and produces file filename. |
| tar -cf archive.tar dirname | Takes everything from directory dirname and puts it into archive.tar |
| tar -xvf file.tar | Extracts the files |
| tar -zxvf file.tar.gz | Extracts the files from compressed archive |
| tar | Creating and Extracting .tar.gz, .tgz and .tar files. See man tar |
| uncompress | Uncompress compressed files. Uncompress filename.Z |
| unzip file.zip | Extracting .zip files shell command |
| zip | Compress files into.zip |
| rpm2cpio pack.rpm |cpio -ivd | To extract contend of RPM package with name pack. [cpio command : -i -- extract, -d -- make local subdirectories, -v -- verbose] |
| rpm2cpio pack.rpm |cpio -t | To lists all the files in the pack package |
| rpm -qa | To list all RPM packages installed. |
| rpm -e | To remove a package. |
| rpm -Uhv | To install a package. |
Hidden configurations files |
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| .bash_history | The list of executed commands. |
| .bash_login | Treated by bash like .bash_profile if that doesn't exist. |
| .bash_logout | Sourced by bash login shells at exit. |
| .bash_profile | Sourced by bash login shells after /etc/profile |
| .emacs | Read by emacs at startup |
| .profile | Treated by bash like ~/.bash_profile if that and .bash_login don't exist. |
| .vimrc | Default vi-editor configuration file. |
Configuration files |
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| etc | This directory contains most of the basic Linux system-configuration Files. |
| /etc/cron* | Directories in this set contain files that define how the crond utility runs applications on a daily (cron.daily), hourly (cron.hourly), monthly (cron.monthly), or weekly (cron.weekly) schedule. |
| /etc/crontab examples | Minute (0-59) Hour (0-23) Day of Month (1-31) Month (1-12 or Jan-Dec) Day of Week (0-6 or Sun-Sat) Command
30 2 12 * 0,6 command At 2:30AM on the 12th of every month that a Sunday or Saturday falls on. 0 0,12 1 */2 * command At 12am and 12pm on the 1st day of every 2nd month. 0 2 1-10 * * command At 2am on the 1st thru the 10th of each month. 30 12 * * 1,3,5 command At 12:30PM every day, every month, on Mon, Wed, Fri |
| /etc/cups | Contains files used to configure the CUPS printing service. |
| /etc/default | Contains files that set default values for various utilities. For example, the file for the useradd command defines the default group number, home directory, password expiration date, shell, and skeleton directory |
| /etc/init.d | Contains the permanent copies of System V–style run-level scripts. These scripts are often linked to files in the /etc/rc?.d directories to have each service associated with a script started or stopped for the particular run level. The ? is replaced by the run-level number (0 through 6). (Slackware puts its run-level scripts in the /etc/rc.d directory.) |
| /etc/mail | Contains files used to configure your sendmail mail service. |
| /etc/passwd | Holds some user account info including passwords (when not "shadowed"). |
| /etc/security | Contains files that set a variety of default security conditions for your computer. |
| /etc/shadow | Contains the encrypted password information for users' accounts and optionally the password aging information. |
| /etc/skel | Any files contained in this directory are automatically copied to a user’s home directory when that user is added to the system. |
| /etc/sysconfig | Contains important system configuration files that are created and maintained by various services (including iptables, samba, and most networking services). |
| /etc/syslogd.conf | The configuration file for the syslogd daemon. syslogd is the daemon that takes care of logging (writing to disk) messages coming from other programs to the system. |
| /etc/xinetd.d | Contains a set of files, each of which defines a network service that the xinetd daemon listens for on a particular port. |
| /var | Contains variable data like system logging files, mail and printer spool directories, and transient and temporary files. |
| /var/log | Log files from the system and various programs/services, especially login (/var/log/wtmp, which logs all logins and logouts into the system) and syslog (/var/log/messages, where all kernel and system program message are usually stored). |
| /var/log/messages | System logs. The first place you should look at if your system is in trouble. |
| /var/log/utmp | Active user sessions. This is a data file and as such it can not be viewed normally. |
| /var/log/wtmp | Log of all users who have logged into and out of the system. The last command can be used to access a human readable form of this file. |