6. Solutions to Common Miscellaneous Problems

6.1. FTP Transfers Seem to Hang.

FTP transfers that die suddenly are due, apparently, to some form of overrunning buffer. It occurs both with Linux and Microsoft servers. On Linux systems, The problem seems to occur most commonly with the distribution's server software.

If you receive ftp: connection refused errors, then the problem is likely due to a lack of authentication. Refer to ``FTP or Telnet Server Won't Allow Logins..''

One remedy is to be replacing the distribution FTP server with the Linux port of the OpenBSD FTP server. The home page is: http://www.eleves.ens.fr:8080/home/madore/programs/

To install the BSD server, follow the installation instructions, and refer to the manual pages for inetd and inetd.conf. (If you have the newer xinetd, see below.) Be sure to tell inetd to run the BSD daemon alone, not as a subprocess of, for example, tcpd. Comment out the line that begins ``ftp'' in the /etc/inetd.conf file and replace it with a line similar to (if you install the new ftpd in /usr/local/sbin/):

# Original entry, commented out.
#ftp    stream  tcp     nowait  root    /usr/sbin/tcpd /usr/sbin/in.ftpd

# Replacement entry:
ftp     stream  tcp     nowait  root    /usr/local/sbin/ftpd -l

The replacement daemon will become effective after rebooting or sending (as root) a SIGHUP to inetd, e.g.:

# kill -HUP inetd

To configure xinetd, create an entry in /etc/xinetd.d per the instructions in the xinetd.conf manual page. Make sure, again, that the command-line arguments for ftpd are correct, and that you have installed the /etc/ftpusers and /etc/pam.d/ftp files. Then restart xinetd with the command: /etc/rc.d/init.d/xinetd restart. The command should report ``OK,'' and the restart will be noted in the system message log.

6.2. 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 metalab.unc.edu, in /pub/Linux/system/Status/ps/procps-0.99.tgz.

6.3. Netscape Crashes Frequently.

Netscape shouldn't crash, if it and the network are properly configured. Some things to check:

6.4. FTP or Telnet Server Won't Allow Logins.

This applies to server daemons that respond to clients, but don't allow logins. On new systems that have Pluggable Authentication Modules installed, look for a file named, ``ftp,'' or ``telnet,'' in the directory /etc/pam/ or /etc/pam.d/. If the corresponding authentication file doesn't exist, the instructions for configuring FTP and Telnet authentication and other PAM configuration, should be in /usr/doc/pam-<version>. Refer also to the answer for ``FTP server says: ``421 service not available, remote server has closed connection.''.''

If it's an FTP server on an older system, make sure that the account exists in /etc/passwd, especially ``anonymous.''

This type of problem may also be caused a failure to resolve the host addresses properly, especially if using Reverse Address Resolution Protocol (RARP). The simple answer to this is to list all relevant host names and IP addresses in the /etc/hosts files on each machine. ( Refer to the example /etc/hosts and /etc/resolv.conf files in: ``Sendmail Pauses for Up to a Minute at Each Command..'') If the network has an internal DNS, make sure that each host can resolve network addresses using it.

If the host machine doesn't respond to FTP or Telnet clients at all, then the server daemon is not installed correctly, or at all. Refer to the manual pages: inetd and inetd.conf on older systems, or xinetd and xinetd.conf, as well as ftpd, and telnetd.

6.5. How To Keep Track of Bookmarks in Netscape?

This probably applies to most other browsers, too. In the Preferences/Navigator menu, set your home page to Netscape's bookmarks.html file, which is located in the .netscape (with a leading period) subdirectory. For example, if your login name is ``smith,'' set the home page to:


Setting up your personal home page like this will present you with a nicely formatted (albeit possibly long) page of bookmarks when Netscape starts. And the file is automatically updated whenever you add, delete, or visit a bookmarked site.

6.6. The Computer Has the Wrong Time.

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 (now called hwclock in many distributions). Refer to: man 8 clock or man 8 hwclock.

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), Network Time Protocol clients like netdate, getdate, and xntp, or NTP client-server suite like chrony. Refer to: ``How to Find a Particular Application..''

6.7. 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 than 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.

6.8. 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.

6.9. When Adding 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.

6.10. Some Programs (E.g. xdm) Won't Allow Logins.

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 ftp://tsx-11.mit.edu:/pub/linux/sources/usr.bin/shadow/. This is the source code. The binaries are probably in linux/binaries/usr.bin/.

6.11. Some Programs Allow Logins with No Password.

You probably have the same problem as in (``Some Programs (E.g. xdm) Won't Allow Logins.''), 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.

6.12. The Machine Runs Very Slowly with 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 To Upgrade/Recompile a 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'').

6.13. System Only Allows Root Logins.

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.

6.14. The 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, then 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.

Another possible command is an alias, ``sane,'' that can work with generic terminals:

     $ alias sane='echo -e "\\033c";tput is2; \
     > stty sane line 1 rows $LINES columns $COLUMNS'

The alias is enclosed with open quotes (backticks), not single quotes. The line break is included here for clarity, and is not required.

Make sure that $LINES and $COLUMNS are defined in the environment with a command similar to this in ~/.cshrc or ~/.bashrc,

     $ LINES=25; export $LINES; $COLUMNS=80; export $COLUMNS

using the correct numbers of $LINES and $COLUMNS for the terminal.

Finally, the output of ``stty -g'' can be used to create a shell script that will reset the terminal:

  1. Save the output of ``stty -g'' to a file. In this example, the file is named ``termset.'':

              $ stty -g >termset

    The output of ``stty -g'' (the contents of ``termset'') will look something like:


  2. Edit ``termset'' to become a shell script; adding an interpreter and ``stty'' command:

               stty 500:5:bd:8a3b:3:1c:7f:15:4:0:1:0:11:13:1a:0:12:f:17:16:0:0:73

  3. Add executable permissions to ``termset'' and use as a shell script:

               $ chmod +x termset
               $ ./termset

[Floyd L. Davidson, Bernhard Gabler]

6.15. I Screwed Up the 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 ftp://metalab.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).

6.16. I Forgot the root Password.

Note: Incorrectly editing any of the files in the /etc/ directory can severely screw up a system. Please keep a spare copy of any files in case you make a mistake.

If your Linux distribution permits, try booting into single-user mode by typing ``single'' at the BOOT lilo: prompt. With more recent distributions, you can boot into single-user mode when prompted by typing ``linux 1,'' ``linux single,'' or ``init=/bin/bash.''

If the above doesn't work for you, boot from the installation or rescue floppy, and switch to another virtual console with Alt-F1 -- Alt-F8, and then mount the root file system on /mnt. Then proceed with the steps below to determine if your system has standard or shadow passwords, and how to remove the password.

Using your favorite text editor, edit the root entry of the /etc/passwd file to remove the password, which is located between the first and second colons. Do this only if the password field does not contain an ``x,'' in which case see below.

   root:Yhgew13xs:0:0: ...

Change that to:

   root::0:0: ...

If the password field contains an ``x,'' then you must remove the password from the /etc/shadow file, which is in a similar format. Refer to the manual pages: ``man passwd,'' and ``man 5 shadow.''

[Paul Colquhuon, Robert Kiesling, Tom Plunket]

6.17. There's a Huge Security Hole in rm!

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

6.18. lpr and/or lpd 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? ".

6.19. 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.

6.20. How To Get LILO to Boot the Kernel Image.

From kernel versions 1.1.80 on, the compressed kernel image, which is what LILO needs to find, is in arch/i386/boot/zImage, or arch/i386/boot/bzImage when it is built, and is normally stored in the /boot/ directory. The /etc/lilo.conf file should refer to the vmlinuz symbolic link, not the actual kernel image.

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

6.21. How To Make Sure the System Boots after Re-Installing the Operating System.

This should work whether you're re-installing Linux or some other, commercial, operating system:

[Jacques Guy]

6.22. The PCMCIA Card Doesn't Work after Upgrading the Kernel.

The PCMCIA Card Services modules, which are located in /lib/modules/version/pcmcia, where version is the version number of the kernel, use configuration information that is specific to that kernel image only. The PCMCIA modules on your system will not work with a different kernel image. You need to upgrade the PCMCIA card modules when you upgrade the kernel.

When upgrading from older kernels, make sure that you have the most recent version of the run-time libraries, the modutils package, and so on. Refer to the file Documentation/Changes in the kernel source tree for details.

Important: If you use the PCMCIA Card Services, do not enable the Network device support/Pocket and portable adapters option of the kernel configuration menu, as this conflicts with the modules in Card Services.

Knowing the PCMCIA module dependencies of the old kernel is useful. You need to keep track of them. For example, if your PCMCIA card depends on the serial port character device being installed as a module for the old kernel, then you need to ensure that the serial module is available for the new kernel and PCMCIA modules as well.

The procedure described here is somewhat kludgey, but it is much easier than re-calculating module dependencies from scratch, and making sure the upgrade modules get loaded so that both the non-PCMCIA and PCMCIA are happy. Recent kernel releases contain a myriad of module options, too many to keep track of easily. These steps use the existing module dependencies as much as possible, instead of requiring you to calculate new ones.

However, this procedure does not take into account instances where module dependencies are incompatible from one kernel version to another. In these cases, you'll need to load the modules yourself with insmod, or adjust the module dependencies in the /etc/conf.modules file. The Documentation/modules.txt file in the kernel source tree contains a good description of how to use the kernel loadable modules and the module utilities like insmod, modprobe, and depmod. Modules.txt also contains a recommended procedure for determining which features to include in a resident kernel, and which to build as modules.

Essentially, you need to follow these steps when you install a new kernel.

Also look at the questions, How do I upgrade/recompile my kernel? and Modprobe can't locate module, "XXX," and similar messages.

6.23. How To Remove (or Change) the Colors in the ls Display.

The shell command, ``unalias ls,'' should completely unset the configuration that some distributions provide as standard. To change the colors, refer to the ls man page (``man ls'').

6.24. Why Won't a Program Work in the Current Directory?

Because the current directory (i.e., ``.'') is not in the search path, for security reasons, as well as to insure that the correct program versions are used. If an intruder is able to write a file to a world-writable directory, like /tmp, presumably he or she would be able to execute it if the directory were in the search path. The solution to this is to include the directory in the command; e.g., ``./myprog,'' instead of ``myprog.'' Or add the current directory to your PATH environment variable; e.g., ``export PATH=".:"$PATH'' using bash, although this is discouraged for the reasons mentioned above.