Commands
Linux maintains its commands in a number of directories, mainly for security reasons but also for logical reasons, in that directories that have the same name in different parts of the hierachy have the same characteristics. For example, we have already learned that commands stored in am "sbin" directory, irrespective of where it is in the hierachy, can only be executed by the root user, while most generally available commands can be found in one of the "/bin" directories, but commands are found in many other places as well.

The table below shows the command types which correspond to the section numbers of the "man" system:

1. Executable programs or shell commands.
2. System calls (functions provided by the kernel)
3. Library calls (functions provided within program libraries)
4. Special files (usually found in /dev)
5. File formats and conventions, e.g. /etc/passwd
6. Games
7. Miscellaneous (including macro packages and conventions)
8. System administration commands (usually only for root user)
9. Kernel routines (non-standard)

The following list shows some of the commands you may wish to use, together with the "man" section they pertain to shown in brackets:

Command Function arch(1) Print machine architecture. bash(1) GNU Bourne-Again Shell. cat(1) Concatentate files and print on standard output. cd(2) Change current directory. chgrp(1) Change file/directory group ownership. chmod(1) Change file/directory access permissions. chown(1) Change file/directory owner and group. cp(1) Copy files and directories. date(1) Print or set the system date and time. dd(1) Convert and copy a file. df(1) Report filesystem disk space usage. dir(1) List directory contents. dmesg(1) Print or control the kernel ring buffer. dnsdomainname(1) Show the system's DNS domain name. dpkg(8) Medium-level package manager for Debian. echo(1) Display a line of text. ed(1) Line-oriented text editor. egrep(1) Print lines matching a pattern. false(1) Do nothing, unsuccessfully. fgrep(1) Print lines matching a pattern. fuser(1) Identify processes using files or sockets. grep(1) Print lines matching a pattern. gunzip(1) Uncompress a gzipped file. gzexe(1) Compress executable file in place. gzip(1) Compress a file using gzip. hostname(1) Show or set the system's host name. kernelversion(1) Print the major kernel version to standout output. kill(1) Send a signal to terminate a process. ln(1) Make a link between files. loadkeys(1) Load keyboard translation tables. login(1) Login to the system. ls(1) List directory contents. lspci(8) List all PCI devices. mkdir(1) Make directories. mknod(1) Make block or character special files. mktemp(1) Make temporary filename. more(1) File perusal filter for CRT viewing. mount(8) Mount a file system. mountpoint(8) See if a directory is a mountpoint. mt(1) Control magnetic tape drive operation. mt-gnu(1) Control magnetic tape drive operation. mv(1) Move (rename) files. nano(1) Nano's ANOther editor. nano-tiny(1) Nano's ANOther editor (cut-down version). netstat(8) Print network connections, routing tables, interface statistics, masquerade connections and multicast memberships. pidof(8) Find the process ID of a running program. ping(8) Send IMP ECHO_REQUEST packets to network hosts. ps(1) Report a snapshot of the current processes. pwd(1) Print name of current working directory. rbash(1) Restricted Bash. readlink(1) Display value of a symbolic link. rgrep(1) Print lines matching a pattern. rm(1) Remove files or directories. rmdir(1) Remove empty directories. run-parts(8) Run scripts or programs in a directory. sed(1) A stream editor. setpci(8) Configure PCI devices. setserial(8) Get/Set Linux serial port information. sh(1) GNU Bourne-Again Shell (same as bash). sleep(1) Delay for a specified period of time. stty(1) Change and print terminal line settings. su(1) Change user-id or become super-user. sync(1) Flush filesystem buffers. tar(1) The GNU version of the tar archiving utility. tcsh(1) C Shell with file name completion and command line editing. tempfile(1) Create a temporary file in a safe manner. touch(1) Change file date/timestamps. true(1) Do nothing, successfully. umount(8) Unmount file system. uname(1) Print system information. uncompress(1) Uncompress compressed files. vdir(1) List directory contents. vi(1) Vi Improved text editor. xinit(1) X-Window System initialiser. zcat(1) Compress or expand files. zcmp(1) Operating System procedure files. zdiff(1) Compare compressed files. zegrep(1) Search possibly compressed files for a regular expression. zfgrep(1) Search possibly compressed files for a regular expression. zforce(1) Force a '.gz' extension on all gzip files. zgrep(1) Search possibly compressed files for a regular expression. zless(1) File perusal filter for crt viewing of compressed text. zmore(1) File perusal filter for crt viewing of compressed text. znew(1) Recompress .Z files to .gz files.