Frequently Asked Questions - Unix-Linux

How to reset your MySQL password on cse.unl.edu

If you have forgotten your MySQL password, To reset the MySQL password go to https://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.

If you know your old MySQL password, the password can be changed from MySQL workbench or from the MySQL command line interface (CLI). To chance your password from the CLI, connect to cse.unl.edu, run the mysql client, once connected, type 'set password=password('####');' and hit enter. Where '####' denotes the password you wish

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Accessing cse.unl.edu using NoMachine - remote X11 GUI access.

NoMachine is a fast, multi protocol remote access client. Which allows RDP and X11 type connections to a variety of servers. We have a NX server installed on cse.unl.edu, which will allow GUI X11 access to cse.unl.edu. Below are steps on setting up a noMachine connection to cse.unl.edu

You can download and installed noMachine from https://www.nomachine.com/ 

To configure a new connection, after you launch noMachine: 

1. from the Recent connections pane,  click on ‘New’ 
2. for Protocol select NX 
3. In the Host input enter ‘cse.unl.edu’
4. for Authentication method select Password
5. select the Don’t use proxy radio button.
6. Name your connection and finally click on Done

Once you have configured a connection to establish a connection:

1. from the Recent connections pane,  double click on the named connection
2. Enter your cse.unl.edu username and password
3. Double click on the Create a new virtual desktop  icon 
4. Click thru the next four dialogs that provide you an overview on using noMachine

Tip: You can save your password, the connection type, and click on Don’t show this message again on the dialogs for one-click connection to cse.unl.edu

Note: Please log off when you are done working on cse.unl.edu. Simply disconnecting the NoMachine client will consume resources on the server and your session will be forcefully quit at somepoint, possibly resulting in loss of any unsaved data or settings.

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Code Development on the CSE Linux server with Visual Studio Code

If you are trying to develop C or C++ code on the CSE server (cse.unl.edu) and using a Windows 10 PC or Mac, you may benefit from using Visual Studio Code (https://code.visualstudio.com/docs/setup/windows (Links to an external site.)) as an editor.  While not as full-featured as a true IDE, VS Code does give you syntax and code error highlighting which can be beneficial.

After installing VS Code using the above link, you will need to install the SFTP extension.  Use the 'Preferences'  link from the VS Code menu to access the Extensions (Mac view:)

VS Code will then open the left-panel showing the extensions.  Into the search window, enter 'ssh' to find the Remote - SSH extension and install it.

With Remote - SSH installed, you now need to modify the settings.json file with the configuration required for Remote - SSH. Press function key F1 and enter Preferences:json at the prompt:

This opens an editor window.  This file dictates how Remote - SSH communicates with a remote.  Add the lines shown:

The "showLoginTerminal": true, option opens a shell prompt to the Linux host and is optional.

With these settings you can initiate a connection by clicking on the Remote Explorer icon and the connect to server icons, labeled 1 and 2  below:

This causes a new window to open with a connection to the cse.unl.edu server.  The indication that you are connected can be seen in the lower left-corner.

Now you can Open a folder..., create a new file, or otherwise edit any file you have access to on the CSE server.

Compilation or execution of your source code can be done from within any 'ssh' session to the CSE server, including the login window displayed by Remote - SSH configuration setting with settings.json.  See the accompanying section on compilers and interpreters.

Disk Usage Considerations

Using the Remote - SSH extension triggers the installation of a 100MB+ image of the VS Code Server into your home directory. Under certain conditions, you may have multiple copies of the VS Code Server application being placed in a subdirectory of your home directory. This appears to be caused by using a login shell other than 'bash', resulting in errors in the VS Code Server scripts appearing in the log files. These old/extra copies count against your disk quota on the CSE server, and may result in you receiving disk quota exceeded emails from CSE Systems Support. These old/extra copies can safely be removed, an easy way to tell is if the date reported by 'ls -lt' is the most recent, that is the copy to keep. All older copies can be safely removed.

Example, below is an example of what you will find in the VS Code Server directory and how to remove it:

wmotycka@cse:~> ls -la  ~/.vscode-server/
total 36
drwxr-xr-x  5 wmotycka staff  4096 Oct 15 12:11 .
drwxr-xr-x 82 wmotycka ugrad 12288 Oct 15 12:18 ..
-rw-r--r--  1 wmotycka staff  2003 Sep 29 15:00 .78a4c91400152c0f27ba4d363eb56d2835f9903a.log
drwxr-xr-x  4 wmotycka staff  4096 Sep 29 15:03 bin
drwxr-xr-x  5 wmotycka staff  4096 Sep 29 14:08 data
-rw-r--r--  1 wmotycka staff   961 Oct 15 12:10 .e5e9e69aed6e1984f7499b7af85b3d05f9a6883a.log
drwxr-xr-x  2 wmotycka staff  4096 Sep 29 14:08 extensions
wmotycka@cse:~>  # USE 'du' TO EXAMINE WHERE THE DISK SPACE IS BEING USED
wmotycka@cse:~> du -hd2 .vscode-server/
104M	.vscode-server/bin/78a4c91400152c0f27ba4d363eb56d2835f9903a
112M	.vscode-server/bin/e5e9e69aed6e1984f7499b7af85b3d05f9a6883a
215M	.vscode-server/bin
20K	.vscode-server/data/User
4.0K	.vscode-server/data/Machine
200K	.vscode-server/data/logs
232K	.vscode-server/data
4.0K	.vscode-server/extensions
216M	.vscode-server/
wmotycka@cse:~> # Remove the extra/oldest copy/copies of the VS Code Server using 'rm -r'
wmotycka@cse:~> rm -r ~/.vscode_server/bin/78a4c91400152c0f27ba4d363eb56d2835f9903a*
wmotycka@cse:~>

The last command above removes the oldest copy of VS Code Server image, keeping the most recently dated copy present.

Where you install VS Code extensions is also important. Extensions stored on the server can use a lot of disk space, and also count against your quota. To add to the pain, VS Code Server seems to build a cached copy of the extensions installed on the server, with a near doubling of used disk space. Further, after uninstalling the software from the server using the VS Code client, the extensions on server persist. It is recommended that you should avoid installing extensions on the server unless necessary.

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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

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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.

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MySQL Database Account - Requesting & Connecting

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 on cse.unl.edu, 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.

To connect to a MySQL database from the command-line from another computer with the mysql command line client installed. Run 'mysql -h cse.unl.edu -u YOUR_CSE_LOGIN -p' and hit enter. Note: the password you will be prompted for will be your MySQL password, which is different from your CSE password.

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