Quick fixes for common Linux problems

Fix Linux driver problems

Don't expect to find Linux drivers on the CD that comes with your shiny new gizmo. That's not because the manufacturers don't care about Linux but because drivers for most devices are already installed on your system as kernel modules. Kernel modules can be loaded from the command line or a startup file, but the HAL/D-BUS system usually recognises hardware and loads the modules automatically. What do you do if it does not? How do you know which module to load?

Identifying the hardware

The first step is to get the details of the hardware with lspci for internal devices or lsusb for USB devices (some laptop hardware is also connected via USB) with these commands

sudo lspci
sudo lsusb

which produce output like

00:1f.2 SATA controller: Intel Corporation 82801HR/HO/HH (ICH8R/DO/DH) 6 port SATA AHCI Controller (rev 02)
01:00.0 VGA compatible controller: nVidia Corporation GeForce 7100 GS (rev a1)
02:00.1 IDE interface: JMicron Technologies, Inc. JMicron 20360/20363 AHCI Controller (rev 03)
03:00.0 Ethernet controller: Attansic Technology Corp. L1 Gigabit Ethernet Adapter (rev b0)

and

Bus 001 Device 004: ID 03f0:2c17 Hewlett-Packard
Bus 004 Device 002: ID 051d:0002 American Power Conversion Uninterruptible Power Supply
Bus 002 Device 002: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port

Once you've identified which device is which, you can get further information by using the -s option to query a specific device and -v for more information, like

sudo lspci -s 03:00.0 -v
sudo lsusb -s 001:004 -v

This is particularly useful with lspci, as the extra information shows the kernel module in use for the device (if there is one). The -k option also shows this, without the other extra information. You may be wondering what use that could be if you're trying to find out which module to load to enable the device.

The answer lies with that firm favourite of troubleshooters, the Live CD. If the device is recognised when booting from the Live CD, run lspci -k to see which module it uses, then you can go back to your installed system and try to load it with.

modprobe -v modulename

If you see no output, the module is already loaded, and should show up in the output from lsmod. If you see something like this:

insmod /lib/modules/.../modulename.ko

the module is now loaded and your drivers should work, or at least be available for configuration. The other responses are a 'device not present' message, which indicates that the hardware for that module is not found, which usually means you have picked the wrong module.

Finally a 'module not found' message means the module is not present on your system. Most distros come with most kernel modules installed, so your hardware is either incredibly arcane and you'll need to compile a new kernel to enable it, or the hardware is only supported in a more recent kernel than you have.

You can check the kernel version of the Live CD and your system with

uname -r

If the Live CD's kernel is newer, look for an update for your distro. Another option is that this hardware is not supported in the kernel but uses a third-party driver. The most common occurrence of this is with wireless cards that use a driver like MadWifi or NdisWrapper. If you need to install a separate driver, it is probably available in one of your distro's repositories. Once that is installed, your hardware should be ready to go.

Graphics hardware

None of the above applies to graphics cards. Their drivers are part of the X.org software, unless you use an ATI or Nvidia card. These do have drivers included with X.org, but the separate driver packages from the manufacturers give better performance. If you want to do anything that needs 3D acceleration, whether it's playing games or enabling desktop effects, you should try the manufacturer's drivers.

While they can be downloaded and installed from the respective websites, it is best to use your package manager to install them, because they also require changes to your xorg.conf file, the file that controls your graphical display, and the distro packages will make the changes for you. If you do decide to go the independent route, make sure you download the correct package for your card and read the instructions carefully before you do anything.

It's not all down to the software

The hardest problems to diagnose are those that occur apparently randomly, especially if they lock up or crash the computer without warning. When the crash occurs at the same time, or using the same software, you have an idea who to blame, but if it is truly random it may well be hardware. The most common hardware causes of such problems are overheating, faulty memory or poor power.

It's no use thinking "this doesn't happen in my other OS, so it must be Linux's fault" because different systems work the hardware differently. For instance, Linux uses memory more aggressively and will experience instability due to faulty memory before Windows starts to show symptoms. Fans and heatsinks become gradually blocked with dust and other crud during a computer's lifetime. Try blowing it clear with a can of compressed air. Installing lm_sensors (your distro should have it) will let you monitor CPU and case temperatures, and a system monitor like GKrellM will display the temperatures on your desktop.

Laptops don't lend themselves to being opened up for a good blow, but you should check the various vents for any blockage. One area where laptops are fairly safe is power, since the battery ensures a clean steady supply. Desktop power supplies are another matter, especially the cheap, unnamed ones that are included with lower-priced cases.

Built down to a price, some barely meet their specs when new, so try a different PSU in your computer – you may be surprised by the difference it makes. Dirty power can damage your hardware and data, so saving money here can be a false economy whereas good-quality PSUs can go on for years. If you live in an area with unreliable or dirty power, a UPS (Uninteruptible Power Supply) may be a worthwhile investment. Surge protectors don't protect against power reductions, only surges.

Testing memory is easy, if time consuming. Most Live CDs include Memtest86, which does exactly what it says. You need to boot into Memtest86, because it can only test memory that isn't in use, so you don't want a full OS running. Let it run through its full set of tests at least twice, preferably overnight. The longer you can leave it running, the more certain you can be that your memory is OK. If you see any errors, at least one of your memory sticks will need to be replaced.

Where's my desktop?

So you've installed the latest distro, rebooted your computer and instead of the glorious 3D enhanced desktop you expected to see, all you get is a black screen with a login prompt and a blinking cursor. What went wrong? The usual cause of this is that the installer was unable to auto-detect the properties of either your graphics card or display.

Sometimes it will drop right down to a text console, other systems may boot into a limited display, like 800x600 with no acceleration. You need to run your distro's configuration tool to generate a working display configuration, but the first step is to log in as root if possible, otherwise as your normal user, using the password you gave during installation. The program to run depends on your distro, but the most popular options are

These usually open a textual version of the graphical configuration tool, from where you can select the correct graphics card and monitor. If your distro doesn't have such a tool, you can create a basic X.org with

X -configure

If you still get a text display when you boot up, log in at the console and run

startx

which should load up a really basic desktop. Press Ctrl+Alt+Backspace to exit it, you now have a working X display. If startx fails, look at the log file at

/var/log/ Xorg.0.log

in particular any lines containing (EE), as these are errors. The file is quite long, but you can find them with

grep EE /var/log/Xorg.0.log

If you get a desktop, but in a limited resolution, the approach is the same, except you can use the graphical versions of the configuration tools.

Fix Linux wireless networking problems

If there is one topic that causes more tearing out of hair than any other, it's wireless networking, what with in-kernel and third-party modules, not to mention the use of Windows drivers as a last resort. Then you have the various encryption methods and a variety of network management systems to contend with.

As with all such things, when you break it down into simple steps, one complex task becomes a series of much simpler ones. The first step is to make sure your hardware drivers are loaded, so check the output of

sudo ifconfig -a

This should show your wired network interface as eth0 and your wireless as one of wlan0, ath0 or even eth1. If none of these show up, try repeating the test from a Live CD and, if it does show up, run

sudo lspci -k

to see which module it uses. If you're still stuck, the details from lspci -v should give enough information on the card to search the web for the correct driver.

Once you have the correct driver you can get on with configuring it, right? Well, maybe. Some wireless cards need a firmware file that is loaded on to the card when it is initialised. The driver will take care of this, but it needs the file to be in /lib/firmware. The methods for getting this file depend on the hardware in use, but usually involve extracting the firmware from the Windows drivers (or downloading a file that someone has already extracted).

So now you are ready to proceed with configuring the connection, so you can skip over the next bit. A last resort? What happens if you can't find the driver for your wireless card? In that case you will have to use NdisWrapper. This is a kernel module that uses the NDIS (Network Driver Interface Specification) drivers supplied for Windows in Linux.

The first step is to install NdisWrapper from your distro's package manager. Then you need files from the CD that came with your card. It is important to use the correct CD, because manufacturers have a habit of changing the chipsets used on a card, and hence the drivers needed, without changing the model number. You can also find information on which cards are supported by which drivers at http://burnthesorbonne. com/?page_id=32.

Once you have installed NdisWrapper, find the driver file, which will be an INF file on the CD. Load it with

sudo ndiswrapper -i /path/to/driver.inf

You can then check that it is working with

sudo ndiswrapper -l

which will list the drivers now available to NdisWrapper. Finally, you can load the module with

sudo modprobe -v ndiswrapper

and your wireless card should appear as wlan0. If there is no INF file on the CD, the drivers are probably packed into an EXE file, which is usually a self-extracting zip file in a Windows executable. You can unpack this using the unzip program on Linux with something like

unzip /mnt/cdrom/install.exe

You will probably want the NdisWrapper module loaded automatically – see the Auto Loading Modules boxout, belowleft, for details on this. Getting connected The first rule of wireless networking is to always use an encrypted connection, but in this case it is easier if you turn off encryption for a couple of minutes, as it removes one potential source of problems. Also make sure that your router is not set to filter out all but specified MAC addresses (we've all been caught out by that one when using a new laptop or wireless card).

Most Linux distros use Network Manager to handle wireless (and wired) connections, and the name of your wireless access point should appear when you click on the Network Manager icon in the task bar. If it doesn't, the first thing to check is that your access point is set to broadcast its SSID (Service Set Identifier – the name of your wireless network). Some people disable this in their access points in the belief that it increases security (it doesn't, because every time you connect to the network, you broadcast the SSID in plain text).

If it still fails to show up, try moving closer to the access point. You can also check for the presence of available networks with these terminal commands

sudo ifconfig wlan0 up
sudo iwlist wlan0 scan

The first line ensures that the wireless card is active, and the second should produce a list of all wireless networks in range. If you see a message like "Interface Doesn't Support Scanning" you're either using the wrong interface (wired instead of wireless), or you're not using the correct driver or firmware for your wireless card, and you'll have to go back to the top of the page and try again.

Once you can connect, immediately disconnect, enable encryption in your access point/router and try again. The best encryption to use is WPA2 or, if your wireless card/ driver does not support it, use WPA (Wi-Fi Protected Access). You should not use WEP unless you absolutely cannot avoid it. It provides only minimal security and is easily cracked by a determined neighbour.