6. Solutions to common miscellaneous problems.


6.1 free dumps core.

In Linux 1.3.57 and later, the format of /proc/meminfo was changed in a way that the implementation of free doesn't understand.

Get the latest version, from sunsite.unc.edu, in /pub/Linux/system/Status/ps/procps-0.99.tgz.


6.2 My clock is very wrong.

There are two clocks in your computer. The hardware (CMOS) clock runs even when the computer is turned off, and is used when the system starts up and by DOS (if you use DOS). The ordinary system time, shown and set by ``date,'' is maintained by the kernel while Linux is running.

You can display the CMOS clock time, or set either clock from the other, with /sbin/clock program--see ``man 8 clock.''

There are various other programs that can correct either or both clocks for system drift or transfer time across the network. Some of them may already be installed on your system. Try looking for adjtimex (corrects for drift), netdate, and getdate (get the time from the network), or xntp (accurate, full-featured network time daemon).


6.3 Setuid scripts don't seem to work.

That's right. This feature has been disabled in the Linux kernel on purpose, because setuid scripts are almost always a security hole. Sudo and SuidPerl can provide more security that setuid scripts or binaries, especially if execute permissions are limited to a certain user ID or group ID.

If you want to know why setuid scripts are a security hole, read the FAQ for comp.unix.questions.


6.4 Free memory as reported by free keeps shrinking.

The ``free'' figure printed by free doesn't include memory used as a disk buffer cache--shown in the ``buffers'' column. If you want to know how much memory is really free add the ``buffers'' amount to ``free''--newer versions of free print an extra line with this info.

The disk buffer cache tends to grow soon after starting Linux up. As you load more programs and use more files, the contents get cached. It will stabilize after a while.


6.5 When I add more memory, the system slows to a crawl.

This is a common symptom of a failure to cache the additional memory. The exact problem depends on your motherboard.

Sometimes you have to enable caching of certain regions in your BIOS setup. Look in the CMOS setup and see if there is an option to cache the new memory area which is currently switched off. This is apparently most common on a '486.

Sometimes the RAM has to be in certain sockets to be cached.

Sometimes you have to set jumpers to enable caching.

Some motherboards don't cache all of the RAM if you have more RAM per amount of cache than the hardware expects. Usually a full 256K cache will solve this problem.

If in doubt, check the manual. If you still can't fix it because the documentation is inadequate, you might like to post a message to comp.os.linux.hardware giving all of the details--make, model number, date code, etc., so other Linux users can avoid it.


6.6 Some programs (e.g. xdm) won't let me log in.

You are probably using non-shadow password programs and are using shadow passwords.

If so, you have to get or compile a shadow password version of the programs in question. The shadow password suite can be found at tsx-11.mit.edu:/pub/linux/sources/usr.bin/shadow/. This is the source code. The binaries are probably in linux/binaries/usr.bin/.


6.7 Some programs let me log in with no password.

You probably have the same problem as in `` Some programs (e.g. xdm) won't let me log in. '', with an added wrinkle.

If you are using shadow passwords, you should put a letter `x' or an asterisk in the password field of /etc/passwd for each account, so that if a program doesn't know about the shadow passwords it won't think it's a passwordless account and let anyone in.


6.8 My machine runs very slowly when I run GCC / X / ...

You may have too little real memory. If you have less RAM than all the programs you're running at once, Linux will swap to your hard disk instead and thrash horribly. The solution in this case is to not run so many things at once or buy more memory. You can also reclaim some memory by compiling and using a kernel with less options configured. See `` How do I upgrade/recompile my kernel? ''.

You can tell how much memory and swap you're using with the free command, or by typing:

cat /proc/meminfo
If your kernel is configured with a RAM disk, this is probably wasted space and will cause things to go slowly. Use LILO or rdev to tell the kernel not to allocate a RAM disk (see the LILO documentation or type man rdev).


6.9 I can only log in as root.

You probably have some permission problems, or you have a file /etc/nologin.

In the latter case, put rm -f /etc/nologin in your /etc/rc.local or /etc/rc.d/* scripts.

Otherwise, check the permissions on your shell, and any file names that appear in error messages, and also the directories that contain these files, up to and including the root directory.


6.10 My screen is all full of weird characters instead of letters.

You probably sent some binary data to your screen by mistake. Type echo '\033c' to fix it. Many Linux distributions have a command, ``reset,'' that does this.

If that doesn't help, try a direct screen escape command.

echo <Ctrl-V><Ctrl-O>
This resets the default font of a Linux console. Remember to hold down the Control key and type the letter, instead of, for example, `Ctrl-V'. The sequence
echo <Ctrl-V><Esc>c
causes a full screen reset. If there's data left on the shell command line after typing a binary file, press Ctrl-C a few times to restore the shell command line.

[Bernhard Gabler]


6.11 I have screwed up my system and can't log in to fix it.

Reboot from an emergency floppy or floppy pair. For example, the Slackware boot and root disk pair in the install subdirectory of the Slackware distribution.

There are also two, do-it-yourself rescue disk creation packages in sunsite.unc.edu/pub/Linux/system/Recovery. These are better because they have your own kernel on them, so you don't run the risk of missing devices and file systems.

Get to a shell prompt and mount your hard disk with something like

mount -t ext2 /dev/hda1 /mnt
Then your file system is available under the directory /mnt and you can fix the problem. Remember to unmount your hard disk before rebooting (cd somewhere else first, or it will say it's busy).


6.12 I've discovered a huge security hole in rm!

No you haven't. You are obviously new to Unix and need to read a good book to find out how things work. Clue: the ability to delete files under Unix depends on permission to write in that directory.


6.13 lpr(1) and/or lpd(8) don't work.

First make sure that your /dev/lp* port is correctly configured. Its IRQ (if any) and port address need to match the settings on the printer card. You should be able to dump a file directly to the printer.

cat the_file >/dev/lp1
If lpr gives you a message like ``myname@host: host not found,'' it may mean that the TCP/IP loopback interface, lo, isn't working properly. Loopback support is compiled into most distribution kernels. Check that the interface is configured with the ifconfig command. By Internet convention, the network number is, and the local host address is If everything is configured correctly, you should be able to telnet to your own machine and get a login prompt.

Make sure that /etc/hosts.lpd contains the machine's host name.

If your machine has a network-aware lpd, like the one that comes with LPRng, make sure that /etc/lpd.perms is configured correctly.

Also look at the Printing-HOWTO `` Where can I get the HOWTO's and other documentation? ''.


6.14 Timestamps on files on MS-DOS partitions are set incorrectly.

There is a bug in the program ``clock'' (often found in /sbin). It miscounts a time zone offset, confusing seconds with minutes or something like that. Get a recent version.


6.15 How do I get LILO to boot the vmlinux file?

>From kernel versions 1.1.80 on, the compressed kernel image, which is what LILO needs to find, is in arch/i386/boot/zImage. The vmlinux file in the root directory is the uncompressed kernel, and you shouldn't try to boot it.

This was changed to make it easier to build kernel versions for several different processors from one source tree.