Commands and Keywords that every Linux user MUST know Part 2

Here is the list of keywords and phrases that every Linux newbie should learn or at least have on file Part 2 :

fmt --  simple optimal text formatter.
Reformat each paragraph in the FILE(s), writing to standard output.

fold -- wrap each input line to fit in specified width.
Wrap input lines in each FILE (standard input by default), writing to standard output.

format -- Format a string in the style of sprintf.
This command generates a formatted string in the same way as the ANSI C sprintf procedure (it uses sprintf in its implementation). FormatString indicates how to format the result, using % conversion specifiers as in sprintf, and the additional arguments, if any, provide values to be substituted into the result. The return value from format is the formatted string.

free -- Display amount of free and used memory in the system.
free displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel. The shared memory col� umn should be ignored; it is obsolete.

fsck* -- check and repair a Linux file system.
*it needs to be executed as SuperUser a.k.a root
fsck is used to check and optionally repair one or more Linux file systems.

ftp -- Internet file transfer program.
Ftp is the user interface to the Internet standard File Transfer Protocol. The program allows a user to transfer files to and from a remote network site.

gawk -- finds and replace text in a file.
Gawk is the GNU Project's implementation of the AWK programming language. It conforms to the definition of the language in the POSIX 1003.1 Standard.

getopts -- parse utility options.
getopts utility will retrieve options and option-arguments from a list of parameters.

grep -- print lines matching a pattern.
grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a match to the given PATTERN. By default, grep prints the matching lines.

groups -- display current group names.
The groups command displays the current group names or ID values. If the value does not have a corresponding entry in /etc/group, the value will be displayed as the numerical group value. The optional user parameter will display the groups for the named user.

groupadd -- create a new group.
The groupadd command creates a new group account using the values specified on the command line plus the default values from the system. The new group will be entered into the system files as needed.

groupdel -- delete a group.
The groupdel command modifies the system account files, deleting all entries that refer to group. The named group must exist. You must manually check all file systems to insure that no files remain with the named group as the file group ID.

groupmod -- modify an existing group definition on the system.
The groupmod command modifies the definition of the specified GROUP by modifying the appropriate entry in the group database.

gzip/gunzip -- compress/decompress files
Gzip reduces the size of the named files using Lempel-Ziv coding (LZ77). Whenever possible, each file is replaced by one with the extension .gz, while keeping the same ownership modes, access and modification times. (The default extension is -gz for VMS, z for MSDOS, OS/2 FAT, Windows NT FAT and Atari.) If no files are specified, or if a file name is "-", the standard input is compressed to the standard output. Gzip will only attempt to compress regular files. In particular, it will ignore symbolic links.

hash --  remember or report utility locations.
The hash utility shall affect the way the current shell environment remembers the locations of utilities found as described in Command Search and Execution . Depending on the arguments specified, it shall add utility locations to its list of remembered locations or it shall purge the contents of the list. When no arguments are specified, it shall report on the contents of the list.

head -- output the first part of files.
Print the first 10 lines of each FILE to standard output. With more than one FILE, precede each with a header giving the file name. With no FILE, or when FILE is -, read standard input.

history -- GNU History Library/ shows the terminal history.
Many programs read input from the user a line at a time. The GNU History library is able to keep track of those lines, associate arbitrary data with each line, and utilize information from previous lines in composing new ones.

hostname -- show or set the system's host name.
Hostname is the program that is used to either set or display the current host, domain or node name of the system. These names are used by many of the networking programs to identify the machine. The domain name is also used by NIS/YP.

id -- print real and effective user and group IDs.
Print user and group information for the specified USERNAME, or (when USERNAME omitted) for the current user.

if -- "use" a Perl module if a condition holds.

ifconfig* -- configure a network interface.
*it needs to be executed as SuperUser a.k.a. root
Ifconfig is used to configure the kernel-resident network interfaces. It is used at boot time to set up interfaces as necessary. After that, it is usu� ally only needed when debugging or when system tuning is needed. If no arguments are given, ifconfig displays the status of the currently active interfaces. If a single interface argument is given, it displays the sta� tus of the given interface only; if a single -a argument is given, it displays the status of all interfaces, even those that are down. Otherwise, it con� figures an interface.

init* -- process control initialization.
*it needs to be executed as SuperUser a.k.a root
Init is the parent of all processes. Its primary role is to create processes from a script stored in the file /etc/inittab . This file usually has entries which cause init to spawn gettys on each line that users can log in. It also controls autonomous processes required by any particular system.

info -- read Info documents.
Read documentation in Info format.

install -- copy files and set attributes.
This install program copies files (often just compiled) into destination locations you choose. If you want to download and install a ready-to-use package on a GNU/Linux system, you should instead be using a package manager like yum, emerge, packman or apt-get.

jobs -- display status of jobs in the current session.
The jobs utility shall display the status of jobs that were started in the current shell environment.

join -- join lines of two files on a common field.
For each pair of input lines with identical join fields, write a line to standard output. The default join field is the first, delimited by whitespace. When FILE1 or FILE2 (not both) is -, read standard input.

kill -- kill a process.
The default signal for kill is TERM. Use -l or -L to list available signals. Particularly useful signals include HUP, INT, KILL, STOP, CONT, and 0. Alternate signals may be specified in three ways: -9 -SIGKILL -KILL. Negative PID values may be used to choose whole process groups; see the PGID column in ps command output. A PID of -1 is special; it indicates all processes except the kill process itself and init.

last --  show listing of last logged in users.
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. Names of users and tty's can be given, in which case last will show only those entries matching the arguments. Names of ttys can be abbreviated, thus last 0 is the same as last tty0. When last catches a SIGINT signal (generated by the interrupt key, usually control-C) or a SIGQUIT signal (generated by the quit key, usually control-\), last will show how far it has searched through the file; in the case of the SIGINT signal last will then terminate. The pseudo user reboot logs in each time the system is rebooted. Thus last reboot will show a log of all reboots since the log file was created. Lastb is the same as last, except that by default it shows a log of the file /var/log/btmp, which contains all the bad login attempts.

less -- opposite of more, output a file page by page with lines numbering.
Less is a program similar to more, but which allows backward movement in the file as well as forward movement. Also, less does not have to read the entire input file before starting, so with large input files it starts up faster than text editors like vi. Less uses termcap (or terminfo on some systems), so it can run on a variety of terminals. There is even limited support for hardcopy terminals. (On a hardcopy terminal, lines which should be printed at the top of the screen are prefixed with a caret.) Commands are based on both more and vi. Commands may be preceded by a decimal number, called N in the descriptions below. The number is used by some com� mands, as indicated.

ln -- make links between files.
In the 1st form, create a link to TARGET with the name LINK_NAME. In the 2nd form, create a link to TARGET in the current directory. In the 3rd and 4th forms, create links to each TARGET in DIRECTORY. Create hard links by default, symbolic links with --symbolic. When creating hard links, each TARGET must exist. Symbolic links can hold arbitrary text; if later resolved, a relative link is interpreted in relation to its parent directory.

logname -- print user´s login name.
logname prints the calling user's name, as found in a system-maintained file (often `/var/run/utmp' or `/etc/utmp'), and exits with a status of 0. If there is no entry for the calling process, `logname' prints an error message and exits with a status of 1.

logout -- write utmp and wtmp entries. exits from shell.

look -- display lines beginning with a given string (lists words that start with certain letters).
The look utility displays any lines in file which contain string as a prefix. As look performs a binary search, the lines in file must be sorted (where sort(1) got the same options -d and/or -f that look is invoked with). If file is not specified, the file /usr/share/dict/words is used, only alphanumeric characters are compared and the case of alphabetic characters is ignored.

lpc -- line printer control program.
lpc provides limited control over printer and class queues provided by CUPS. It can also be used to query the state of queues. If no command is specified on the command-line, lpc will display a prompt and accept commands from the standard input.

lpq --  show printer queue status.
lpq shows the current print queue status on the named printer. Jobs queued on the default destination will be shown if no printer or class is specified on the command-line.

lpr -- print files.
lpr submits files for printing. Files named on the command line are sent to the named printer (or the system default destination if no destination is spec� ified). If no files are listed on the command-line, lpr reads the print file from the standard input.

ls -- list directory contents.
List information about the FILEs (the current directory by default). Sort entries alphabetically.

m4 -- macro processor.
Process macros in FILEs. If no FILE or if FILE is `-', standard input is read.

mail -- send and receive mail.
mail is an intelligent mail processing system which has a command syntax reminiscent of ed(1) with lines replaced by messages.

man -- format and display the on-line manual pages.
man formats and displays the on-line manual pages. If you specify section, man only looks in that section of the manual. name is normally the name of the manual page, which is typically the name of a command, function, or file. However, if name contains a slash (/) then man interprets it as a file specifi� cation, so that you can do man ./foo.5 or even man /cd/foo/bar.1.gz.

md5sum -- compute and check MD5 message digest.
Print or check MD5 (128-bit) checksums. With no FILE, or when FILE is -, read standard input.

mesg -- control write access to your terminal.
Mesg controls the access to your terminal by others. It's typically used to allow or disallow other users to write to your terminal.

mkdir -- creates new directory.
mkdir creates each directory NAME in the order given. It reports an error if NAME already exists, unless the `-p' option is given and NAME is a directory.

mkfifo -- make FIFOs (named pipes).
A "FIFO" is a special file type that permits independent processes to communicate. One process opens the FIFO file for writing, and another for reading, after which data can flow as with the usual anonymous pipe in shells or elsewhere.

mknod -- make block or character special files.
Create the special file NAME of the given TYPE.

more -- file perusal filter for crt viewing.
More is a filter for paging through text one screenful at a time. Users should realize that less provides more emulation and extensive enhancements.

mount -- mount a file system.
All files accessible in a Unix system are arranged in one big tree, the file hierarchy, rooted at /. These files can be spread out over several devices. 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.

mtools -- utilities to access DOS disks in Unix.
Mtools is a public domain collection of tools to allow Unix systems to manipulate MS-DOS files: read, write, and move around files on an MS-DOS filesystem (typically a floppy disk). Where reasonable, each program attempts to emulate the MS-DOS equivalent command. However, unnecessary restrictions and oddi� ties of DOS are not emulated. For instance, it is possible to move subdirectories from one subdirectory to another.

mv -- move (rename) files.
mv can move any type of file from one file system to another.

nice -- run a program with modified scheduling priority.
Run COMMAND with an adjusted niceness, which affects process scheduling. With no COMMAND, print the current niceness. Nicenesses range from -20 (most favorable scheduling) to 19 (least favorable).

nl -- number lines of files.
nl writes each FILE (`-' means standard input), or standard input if none are given, to standard output, with line numbers added to some or all of the lines

nohup -- run a command immune to hangups, with output to a non-tty.
nohup runs the given COMMAND with hangup signals ignored, so that the command can continue running in the background after you log out.

passwd -- change user password.
The passwd command changes passwords for user accounts. A normal user may only change the password for his/her own account, while the superuser may change the password for any account. passwd also changes account information, such as the full name of the user, the user´s login shell, or his/her password expiry date and interval.

paste -- merge lines of files.
Write lines consisting of the sequentially corresponding lines from each FILE, separated by TABs, to standard output. With no FILE, or when FILE is -, read standard input.

pathchk -- check whether file names are valid or portable.

ping -- send ICMP ECHO_REQUEST to network hosts.
ping uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from a host or gateway. ECHO_REQUEST datagrams (``pings'') have an IP and ICMP header, followed by a struct timeval and then an arbitrary number of ``pad'' bytes used to fill out the packet.

pr --  convert text files for printing.
pr writes each FILE (`-' means standard input), or standard input if none are given, to standard output, paginating and optionally outputting in multicolumn format; optionally merges all FILEs, printing all in parallel, one per column.

printenv --  print all or part of environment.

printf -- format and print data.
Due to shell aliases and built-in `printf' command, using an unadorned `printf' interactively or in a script may get you different functionality.

ps --  report a snapshot of the current processes.
ps displays information about a selection of the active processes. If you want a repetitive update of the selection and the displayed information, use top(htop) instead.

pwd -- print name of current/working directory.

rcp -- remote file copy.
Rcp copies files between machines. Each file or directory argument is either a remote file name of the form ``rname@rhost:path'', or a local file name (con� taining no `:' characters, or a `/' before any `:'s).
 
read --  read a line from standard input.
The read utility will read a single line from standard input.

readonly -- set the readonly attribute for variables.
The variables whose names are specified shall be given the readonly attribute. The values of variables with the readonly attribute cannot be changed by subsequent assignment, nor can those variables be unset by the unset utility. If the name of a variable is followed by = word, then the value of that vari� able shall be set to word.