Unix and Linux Fundamental Commands

id – print real and effective UIDs and GIDs for user’s terminal.

who – displays a list of users currently logged on to the system.

date – print or set the system date and time.

passwd – update a user’s authentication token(s); change password.

echo – displays a line of text.

banner – prints a large banner on printer.

write – send a message to another specified user.

mesg – controls write access to your terminal by others; EX: mesg [ y : n ]

mail – send and receive mail.

            -v : verbose mode; details of delivery are displayed on user’s terminal.

            -i  :  ignore TTY interrupt signals; useful when using ‘mail’ on noisy phone lines.

            -I  : forces ‘mail’ to run in interactive mode even when input isn’t a terminal.

pwd – print name of current/working directory.

ls – list directory contents.

find – search for files in a directory hierarchy.

mkdir – make directories.

rmdir – remove empty directories.

file – determine file type.

cat – concatenate files and print on the standard output (usually screen).

more – file filter for paging through text one full screen at a time.

man – formats and displays the on-line manual pages.

tail – display the last few lines of a file.

head – display the first few lines of a file.

lp – line printer devices

cp – copy files and directories.

mv – move (rename) files.

ln – make links between files.

rm – remove files or directories.

chmod – change file access permissions.

touch – change file timestamps.

chown – change file owner and group.

chgrp – change group ownership.

su – run a shell with substitute user and group IDs; switch user.

newgrp – log in to a new group.

vi – text editor.

whereis – locate the binary, source, and manual page files for a command.

sort – sort lines of text files.

grep – print lines matching a given pattern.

wc – print the number of bytes, words, and lines in files.

> - redirection symbol – create a new file or overwrite an existing file by attaching it to a command that produces output.

>> - used to append output to an existing file without overwriting that file.

cut – remove sections from each line of file.

tr – translate or delete characters.

tee – read from standard input and write to standard output and files.

pr – convert text files for printing.

ps – report process status.

nohup – run a command immune to hang-ups, with output to a non-TTY.

nice – run a program with modified scheduling priority.

kill – terminate a process.

tar – the GNU version of the tar archiving utility.

cpio – copy files to and from archives.

ftp – user interface to the ARAPNET standard File Transfer Protocol.

telnet – used to communicate with another host using the TELNET protocol.

rlogin – starts a terminal session on a remote host host.

hostname – show or set the system’s host name.

rlp – remote file copy.

clear – clear the terminal screen.

sleep – delay for a specified amount of time.

cal – displays a default or specified calendar.

shutdown – brings the system down in a secure way. All logged-in users are notified that the system is going down and new logins are blocked.

pg – page to control screen scrolling.

diff – find differences between two files.