Computer Laboratory

Introduction

This page is primarily for users of Lab managed Linux machines, though users of self-managed (so called alien machines) may also find useful information here it should be noted that many things on Lab managed machines are different to a default installation of Linux.

Specific information about using SuSE Linux.

System Software

Booting

Most Linux machines use the GRUB boot loader to boot Linux. Some dual boot machines use the Windows NT boot loader to boot GRUB. GRUB will present a list of the available kernels labelled Linux n.n.nn and should default to loading the most recent kernel (with the label Linux.) Hit return to choose the default without waiting for the timeout.

Most recent machine can be woken up by sending it a "WoL" packet. This can normally only be done by a machine on the same VLAN, but a Lab web page allows this to be done from the internet. Some machine also have a BMC which allow more explicit control (such as powering on and off), which can be accessed using a web browser in the Lab. If a user needs such access, contact sys-admin.

Shutting Down

Single-boot Linux machines should be turned off when not needed. As above, most can be rebooted remotely if needed, and the time sharing systems can be used for light use from outside.

If a machine appears unresponsive on the console it can often still be accessed from another machine over the network. In such cases the fault sometimes lies with user software (e.g. Firefox) and the offending process can be stopped using the kill(1) command.

In the event that a machine does require to be shut down for some reason, use one of the following methods:

shutdown -P now
The assigned user of a machine (anyone who can write to /etc/user-config/bundles) can shut the machine down using the command "cl-asuser shutdown -P now". Anyone with full sudo access can use "sudo shutdown -P now".
Control-Alt-Delete
Switch to a virtual console using <Alt>-<Control>-<F1> if in X-windows and press <Control>-<Alt>-<Delete>.
Alt-SysRq-S,U,B
This is for use in the event the machine is unresponsive to keyboard input and cannot be logged in to from the network. It uses the Linux kernel's Magic SysRq key. Whilst holding down <Alt> and <SysRq> press the keys S, U and B, one at a time.
Front panel reset and/or power switch
If none of the above work, it may be necessary to resort to pressing the reset button or even the power switch. This may well corrupt the filesystem (see Problems on Restarting below) so it should only be used if all other methods have been tried and have failed.

On desktop machines the reset switch is normally a button near the on/off button at the front of the system unit. On laptops it is normally a recessed switch behind a very small hole, which needs a biro or some such to press it. Do not use a pencil as the 'lead' may break and is a conductor.

If even the reset button fails, then use the power switch. You may have to hold it for up to 20 seconds before it has any effect.

Problems on Booting

If a machine has been shutdown 'uncleanly' then it may have a corrupt filesystem which requires operator intervention to correct. In this case the reboot stops with a prompt 'Enter root password for system maintenance:' If this happens send e-mail to sys-admin@cl.cam.ac.uk saying what the problem is and which machine it is (it helps of you also state the name and location of the machine.)

X Windows

The graphical user interface on all Unix systems in the lab is X-Windows, originally developed at the Laboratory for Computer Science at MIT. See X(7x)

Virtual Consoles and X

Normally workstations run an X server on the console. In addition to this, virtual consoles 1 to 6 are available for text mode logins. If the X console is showing then pressing <Alt>-<Control>-<Fn> will switch to virtual console n. If a text console is showing then pressing <Alt>-<Fn> will switch to virtual console n. Usually the X server runs on virtual console 7 so to switch back to X from another virtual console press <Alt>-<F7>.

Screen Settings

The X screen resolution, display depth and refresh rate are setup automatically. Usually the default is acceptable but if not then a system administrator can configure a different setting. Send e-mail to sys-admin@cl.cam.ac.uk stating which machine you are using and what resolution/refresh rate and colour depth you require.

Most modern LCDs only operate properly at a fixed resolutionn and refresh rate so it is unusual to need to change this.

The program xrandr allows you to experiment with display settings. To list possible settings type xrandr -q. This will produce someting like

 SZ:    Pixels          Physical       Refresh
*0   1600 x 1200   ( 402mm x 302mm )  *85   75
 1   1400 x 1050   ( 402mm x 302mm )   85   75
 2   1280 x 1024   ( 402mm x 302mm )   85   75
 3   1280 x 960    ( 402mm x 302mm )   85
 4   1152 x 864    ( 402mm x 302mm )   85   75
 5   1024 x 768    ( 402mm x 302mm )   85   75   87
 6    960 x 720    ( 402mm x 302mm )   85   75
 .
 .
 .
 25   320 x 175    ( 402mm x 302mm )   85
Current rotation - normal
Current reflection - none
Rotations possible - normal
Reflections possible - none

To try out a given setting type xrandr -s n where n is one of the SZ: numbers in the listing produced by xrandr -q.

Window Managers and Desktops

X windows does not specify any particular desktop or window manager as other window systems do. This is left to the individual user to choose. See Window managers/Desktop environments for details of the usual Window managers and Desktop environments.

See this page Initialisation files and configurationfor more information on configuring the X working environment.

Removable Media

This section applies only to Lab managed Fedora Core or Red Hat machines. SuSE Linux provides an automounter for removable media accessed via the directory /media, see Using SuSE Linux.

CD ROM Drives

CD ROMS can be mounted using the mount(8) command:

mount /mnt/cdrom

The files will be owned by the user issuing the mount command and that user's primary group. Usually the files are world-readable, so if you are accessing private information from a CD then e-mail sys-admin first, stating the problem and mentioning which machine you are using.

Floppy Disks

Usually the files are world-readable, so if you are accessing private information from a floppy disk then e-mail sys-admin first, stating the problem and mentioning which machine you are using.

MSDOS format floppy disks are easiest accessed and written using the mtools package which provides mdir and mcopy, equivalent to the MSDOS dir and copy commands.

Floppy disks can also be mounted using the mount(8) command:

mount /mnt/floppy

The files will be owned by the user issuing the mount command and that user's primary group.

Ownership of the /dev/fd* devices is according to Unix Device Permissions policy.

USB Devices

Flash memory is typically mounted as /mnt/flash but is specific to devices as different partitioning schemes are used. If you want to use a USB flash memory device as a filesystem then plug the device into the machine you want to use it on and e-mail sys-admin stating which machine it is and what you want to do.

Other devices may or may not be supported according the version of Linux or the kernel running on a particular machine. If you want to use such a device then send e-mail to sys-admin saying which machine you are using and giving as much information about the device as possible, including RPS of any user-space programs that are required.

Other Peripherals

Serial devices

On most Linux workstations there is no default user access to serial devices, though this can be arranged. Again, send mail to sys-admin@cl.cam.ac.uk stating which machine you are using and what device you want to attach.

Sound

If the machine has sound hardware and the kernel supports it then the sound devices are usually made available to the user logging in on the console according to the Unix Device Permissions policy in the case of Fedora or Red Hat Linux and automatically in the case of SuSE Linux.

Applications

There are a huge number of application programs that run under Linux. This section lists only a few of the basic ones that almost everyone uses. If there is a specific application program not on your machine that you want installed then send mail to sys-admin@cl.cam.ac.uk stating the name, version, its purpose and on which machine you want it installed. If possible, provide a URL for the application home page and/or a Red Hat RPM suitable for the version of Red Hat Linux running on your workstation.

e-mail

The supported e-mail user agent is exmh. This is a Tcl/Tk front-end to the nmh(1) programs.

It is recognised that exmh is somewhat baroque and other e-mail clients are under investigation.

Web Browsers

The supported web browsers are Firefox and the text-based lynx(1) browser.

On Lab managed Fedora or Red Hat Linux, the recommended way to start Firefox is to use the wrapper script /usr/X11R6/bin/firefox. This remembers the last used version and runs that by default.

In addition there is GNU wget(1) for retrieving pages from FTP and WWW servers and storing them in local files.

Tex/LaTeX

TeX and LaTeX are fully supported packages. The manual pages are tex(1) and latex(1). If you are new to these then you will need to read a book or two. See the TeX FAQ.

Text Editors

Supported text editors are emacs(1) and vim(1).

GNU Emacs

Type emacs to start emacs in an X-window. Type emacs -nw to start emacs running in the terminal window with a curses style interface. Emacs can be extensively customised via ~/.emacs, see Emacs. If you have problems with emacs please first verify that they are not caused by errors in your ~/.emacs. You can do this by using mv(1) to rename the file to, say ~/.emacs-disabled.

Vim

Type vi to start vim. Vim maintains a file ~/.viminfo of defaults which it updates per session.

Graphics

For lightweight bitmap viewing and basic manipulation use xv(1). It is capable of cropping, colour and contrast transform and format conversions.

For drawing and retouching bitmapped graphics use gimp.

For vector drawing use xfig or, on SuSE machines, Inkskape.