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Linux/UNIX Commands & Apt-get Commands
  
Linux Tutorials: Linux.org | http://www.ctssn.com | ||
A note on hardening Linux: In 2004, the W32.Blaster.Worm and other similar worms were spread by simply surfing on the Internet. Windows is currently more vulnerable to viruses and worms because malware was written to attack the Windows operating system, but as Linux grows in popularity, expect similar problems. "Trojan Horse attacks GNU Project", read the article here. | ||
| ls | Lists files. The equivalent of "dir" in DOS. Common switches are -al which will list all files with a long description, including their permissions, size, and datestamp. You can also type in ls -al followed by a specific filename to learn information about that specific file. This is helpful if you have many files within a directory and you only want information on one of them. You can even use wildcards. For example, ls *.html shows only files with extension .html | |
| uname -a,-s,-r | Show info about the current machine, kernel and operating system. | |
| pwd | Print Working Directory, also Present Working Directory: Wonder which directory you're currently in? pwd reveals the full path. | |
| clear | clear the screen | |
| touch | touch <filename>. If filename doesn't exist it gets created (0 byte). If filename already exists, touch alters its timestamp to the current time. Please note, in UNIX we can not easily name files with spaces in them, so words should use underscores or a capital letter to separate them. For example, touch my file will not work. You must write either touch myFile or touch my_file . This applies to creating directories as well. Other ways to create a new file: cat > newfile and ls > newfile will also create a new file. See redirecting output symbol > below... | |
| mkdir | makes a directory. | |
| rmdir | removes an empty directory. If it is not empty, you can use rm -r <dir name>. | |
| rm | Removes files. You can use it with wildcards too. For example rm -f *.html will remove all html files in the directory. You can use rm to remove a directory with an -r or -rf switch. However, this is not the ideal way to remove directories. | |
| cp | cp originalFile newFile Creates a copy of the first file having the name of the second. If the paths are not specificied, then cp assumes you mean the current working directory. You can also copy a file to another location. For example, cp OriginalFile /home/someDirectory/newFile will copy a file from the current directory to another directory with "NewFile" as it's name. If no name is specified, and you are copying the file to another directory, then the original filename will be used. | |
| file | file tests each argument and tries to classify File Type using three tests performed in this order: filesystem, magic number, and language. The first test that succeeds causes the file type to be printed: text, executable, data and others. In this example, 'x-window-manager' is the argument: Using Debian/Linux shell, from /usr/bin$ file x-window-manager x-window-manager: symbolic link to /etc/alternatives/x-window-manager | |
| ln | Create a link to the specified target with optional link_name. If link_name is omitted, a link with the same base name as the target is created in the current directory. ln -s creates a symbolic link which allows for later removal of the link without removing the original file. Use the rm command: rm <filename> | |
| whatis | whatis searches a set of database files containing short descriptions of system commands for keywords and display the result on the standard output (stdout). Only complete word matches are displayed. | |
| whereis | whereis locates source/binary and manuals sections for specified files. The supplied names are first stripped of leading pathname components and any (single) trailing extension of the form .ext, for example, .c. Prefixes of s. resulting from use of source code control are also dealt with. whereis then attempts to locate the desired program in a list of standard Linux places. | |
| find | find will locate files from a shell command prompt, e.g., find / -name 'FAQ' for a list of FAQ file locations. Enclose the filename in single quotes with the find command. | |
| who | who is using the Linux server at this time. who -a for time of last system boot, active processes spawned by init, dead processes, current run level and lists users logged in. Try who am i and/or who mom likes. Also try ls -last for recent login info on your server. | |
| which | which takes one or more arguments. For each of its arguments it prints to stdout the full path of the executables that would have been executed when this argument had been entered at the shell prompt. It does this by searching for an executable or script in the directories listed in the environment variable PATH using the same algorithm as bash. | |
| echo |
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| wc | The wc command will give you the number of lines, words and letters (characters) in a file and in that order. Example from /var/www directory, type: wc -w index.html will display the word count of index.html. | |
| cal | Cal displays a simple calendar. If arguments are not specified, the current month is displayed. cal -y displays the current year and cal 08 2003 displays the month of August, 2003. If you add the option cal -m, the week will start on Monday, as it is preferred in many countries. Debian: ncal to print a calendar starting on Monday. | |
| date |
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| exit | You can get out of a terminal with the exit command. If you're working in text mode, typing exit will prompt you to login again. If you want to work as another user, use logout instead. If you're in x-windows, exit will close the X-Terminal you're working with. | |
| last | The command last will show you the people who have logged into the computer today and the terminals they are/were using. Last searches back through the file /var/log/wtmp or the file designated by the -f flag and displays a list of all users logged in and out since that file was created. Also try this command: ls -last | |
| mount | The mount command serves to attach the file system found on some device to the big file tree. Conversely, the umount command will detach it again. All files accessible in a Unix system are arranged in one big tree, the file hierarchy is rooted at /. These files can be spread out over several devices. The standard form of the mount command, is mount -t type device dir You can also use the mount command to copy to and from other devices. If you would like to get some files from a CD-ROM, the standard command to do this is:
More from Linux.org: http://www.linux.org/lessons/beginner/l13/lesson13d.html | |
| umount | The umount command detaches the file system(s) mentioned in the file hierarchy. A file system is specified either by giving the directory where it has been mounted, or by giving the special device on which it lives. A file system cannot be unmounted when it is 'busy' - for example, when there are open files on it, or when some process has its working directory there, or when a swap file on it is in use. | |
| cron | cron is a program on Linux systems that allows programs to be run automatically at certain times and under certain conditions. Cron searches /var/spool/cron for crontab files which are named after accounts in /etc/passwd; crontabs found are loaded into memory. | |
