Frequently Asked Questions - Unix-Linux

MySQL Database Account

MySQL is the general purpose database available for student use. Each user is allowed one database. This database is automatically created after requested by a user and is named the same as your cse username. Users can create as many tables as they want but we ask that they keep all databases to a reasonable size.

Requesting a MySQL Account and Database
Any user with a CSE account can request access to the MySQL server running on cse.unl.edu. To do so, log in to the CSE Account Management Utility (AMU) page at cse.unl.edu/account with your CSE account credentials. Once you log in, click the Account Settings link on the left page. From there, check the box for MySQL Account and then click Save. You should then receive an email message with your MySQL account credentials.

Connecting to MySQL Database
To connect to a MySQL database from the command-line, type 'mysql -p' and hit enter. The password you will be prompted for will be your MySQL password, which is different from your CSE password.

Resetting MySQL Password
To reset the MySQL password go to cse.unl.edu/account. Log in using your cse credentials and click the 'Reset MySQL Password' link. A new randomly generated password will be sent to you via email.

Changing MySQL Password from CLI
From the MySQL prompt, type 'set password=password('####');' and hit enter. '####' denotes the password you wish to set it to.

Back to top ↑

Compilers and Interpreters available on cse.unl.edu

Compilers

gcc	GNU CcCompiler
g++	GNU C++ compiler
javac	Java compiler
gfortran	GNU Fortran compiler
clisp	Common Lisp
alisp	Allegro Common Lisp

Interpreters

perl	Perl command line scripting language
php	Command line and web scripting language
ruby	Command line and web scripting language
pyton	Command line scripting language

Back to top ↑

Basic Unix Commands

Note on systax used in document:

items in [] are optional

items in {} can be repeated 0 or more times.

fn = filename (possible with wildcards)

dir = directory name

File System:

cat fn {fn}

concatenate, can be used to display a file.

more fn {fn}

displays file(s) one screenful, at a time. At MORE prompt enter: space bar - for next screenful <cr> - for next line, q - to quit more command.

cp fn1 fn2

copy file - fn1 to fn2, fn1 remains.

mv fn1 fn2

move (rename) file - fn1 to fn2, fn1 no longer exists.

rm fn

remove (delete) file.

lpr -Pprinter_name fn

print a file, printer_name = ps16 or ps17.

ls [fn]

list files in current directory option filename is usually used to display files matching wildcards. (ie. ls *.s will list all assembly language source files.)

ls -lgRa

Recursive listing of all files within all subdirectories. Longest, most descriptive format.

cd [dir]

change working directory, ``home directory" if not specified. cd .. will backup one level in the directory structure.

pwd

print working directory path.

mkdir dir

make a new directory, giving it the name dir (within the current directory)

rmdir dir

remove (delete) the directory named dir (the directory must be empty)

file fn

Tries to determine what kind of information is in a file by consulting the file system index and by reading the file itself.

du

Prints a summary of total space occupied by all files in a hierarchy.

sort fn

Sorts ASCII files line-by-line.

chmod

Change file permissions. See the man pages for a complete description of settings. Use this command to determine whether files can be readable by other people.

find . -name filename

In it's most simple form find will display all files in this and any subdirectories which name matches filename. See the man page for find for a complete description of this command. Find can be use to find files matching name patters, dates, owners, sizes, etc. and to perform action on matched files.

gzip fn

Use this to compress files not needed immediately to conserve disk space. A ``.gz" will be appended to the filename.

gzip -d

Uncompresses files with ``.Z" at end of filename.

head {-n} fn

Prints first n lines of a text file. If no number is specified, the default is 10.

tail {-n} fn

Prints last n lines of a text file. If no number is specified, the default is 10.

tail {-n} fn

Prints last n lines of a text file. If no number is specified, the default is 10.

grep string fn

Print occurrences of string in file

Remote Connection:

ssh remote_host

Launch a secure shell to the remote host specified.

Communication:

finger

list users currently on the system.

who

list users currently on the system.

w

what, similar to who but includes what they are doing.

pine

Email message utility.

pine username

will send Email to username.

talk username

allows two users to have an interactive conversation over the computer.

write username

allows a user to put a message on another users screen.

mesg n

Makes it so other users cannot interrupt you with talk requests, and write messages.

Help:

man command

manual, returns the manual for the given command from the UNIX on-line manual. If you cannot find a man page for a command, there may be one in a directory that isn't in your MANPATH. Your MANPATH is setup in the .login file and a command's man page is usually in a man directory off the same parent directory as the command. For example, if the command is located in /usr/local/bin, its man page is probably in /usr/local/man.

man -k keyword

display manual headings containing the word keyword.

Miscellaneous:

alias name def

Assigns ``def'' to the alias ``name''. Usually found in the .cshrc file. For example ``alias dir ls -la''.

clear

Clears screen.

history

List history of commands used.

!!

re-execute the last command entered.

!x

re-execute the last command that started with the given letter, eg !c will re-execute the last command that began with the letter c.

jobs -l

list all currently stopped or background jobs with job numbers and process ID's.

kill [-signal] %jobnumber

kill the given job number. Use the "jobs" command to show running jobs. You might need to kill a job to logout if you have accidentally put a job into the background or stopped a job. Use -TERM or -KILL singlas to force quite jobs.

kill PID

kill the given Process. refer the "ps" command to find running processes. Use -TERM or -KILL singlas to force quite jobs.

ps -fa

list all your current processes. See the man page for a full description.

<control>C

kill the current process - the one in the  foreground

<control>Z

suspend foreground process.

bg

put a suspended job in the background.

fg

put a suspended or background job in the foreground.

date

display time and date.

To find out about more commands, click  here.

Back to top ↑

Editing a File on Unix with vi - Basic Commands.

What is  vi?

The default editor that comes with the UNIX operating system is called  vi ( visual editor). [Alternate editors for UNIX environments include  pico and  emacs, a product of GNU.]

The UNIX  vi editor is a full screen editor and has two modes of operation:

1. Command mode commands which cause action to be taken on the file, and
2. Insert mode in which entered text is inserted into the file.

In the command mode, every character typed is a command that does something to the text file being edited; a character typed in the command mode may even cause the  vi editor to enter the insert mode. In the insert mode, every character typed is added to the text in the file; pressing the  <Esc> ( Escape) key turns off the Insert mode.

While there are a number of  vi commands, just a handful of these is usually sufficient for beginning  vi users. To assist such users, this Web page contains a sampling of basic  vi commands. The most basic and useful commands are marked with an asterisk ( * or star) in the tables below. With practice, these commands should become automatic.

NOTE: Both UNIX and  vi are  case-sensitive. Be sure not to use a capital letter in place of a lowercase letter; the results will not be what you expect.

To Get Into and Out Of  vi

To Start  vi

To use  vi on a file, type in  vi filename. If the file named  filename exists, then the first page (or screen) of the file will be displayed; if the file does not exist, then an empty file and screen are created into which you may enter text.

To Exit  vi

Usually the new or modified file is saved when you leave  vi. However, it is also possible to quit  vi without saving the file.

Note: The cursor moves to bottom of screen whenever a colon ( :) is typed. This type of command is completed by hitting the  <Return> (or  <Enter>) key.

Moving the Cursor

Unlike many of the PC and MacIntosh editors,  the mouse does not move the cursor within the  vi editor screen (or window). You must use the the key commands listed below. On some UNIX platforms, the arrow keys may be used as well; however, since  vi was designed with the Qwerty keyboard (containing no arrow keys) in mind, the arrow keys sometimes produce strange effects in  vi and should be avoided.

If you go back and forth between a PC environment and a UNIX environment, you may find that this dissimilarity in methods for cursor movement is the most frustrating difference between the two.

In the table below, the symbol  ^ before a letter means that the  <Ctrl> key should be held down while the letter key is pressed.

Screen Manipulation

The following commands allow the  vi editor screen (or window) to move up or down several lines and to be refreshed.

Adding, Changing, and Deleting Text

Unlike PC editors, you cannot replace or delete text by highlighting it with the mouse. Instead use the commands in the following tables.

Perhaps the most important command is the one that allows you to back up and  undo your last action. Unfortunately, this command acts like a toggle, undoing and redoing your most recent action. You cannot go back more than one step.

The main purpose of an editor is to create, add, or modify text for a file.

Inserting or Adding Text

The following commands allow you to insert and add text. Each of these commands puts the  vi editor into insert mode; thus, the  <Esc> key must be pressed to terminate the entry of text and to put the  vi editor back into command mode.

Changing Text

The following commands allow you to modify text.

Deleting Text

The following commands allow you to delete text.

Cutting and Pasting Text

The following commands allow you to copy and paste text.

Other Commands

Searching Text

A common occurrence in text editing is to replace one word or phase by another. To locate instances of particular sets of characters (or strings), use the following commands.

Determining Line Numbers

Being able to determine the line number of the current line or the total number of lines in the file being edited is sometimes useful.

Saving and Reading Files

These commands permit you to input and output files other than the named file with which you are currently working.

Back to top ↑