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Subject: Linux Frequently Asked Questions with Answers (Part 4 of 6)
This article was archived around: 24 May 2006 04:22:39 GMT
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
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
6.13. System Only Allows Root Logins.
You probably have some permission problems, or you have a file
In the latter case, put "rm -f /etc/nologin" in your /etc/rc.local or
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
$ 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
2. Edit "termset" to become a shell script; adding an interpreter and
3. Add executable permissions to "termset" and use as a shell script:
$ chmod +x 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
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.
Change that to:
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
$ 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 127.0.0.0, and the local
host address is 127.0.0.1. 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
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
This should work whether you're re-installing Linux or some other,
commercial, operating system:
* Insert a blank, formatted floppy in drive A:
* Save a copy of the boot hard drive's Master Boot Record to the
floppy, by executing the command:
#dd if=/dev/hda of=/dev/fd0 count=1
dd is a standard program on Linux systems. A MS-Windows compatible
version is available from ftp://ftp.gnu.org/, as well as many MS
* Test that the floppy boots the system by rebooting with the floppy
in the A: drive.
* Then you should be able to install the other operating system (on
a different hard drive and/or partition, if you don't want to
* After installation, boot Linux again from the floppy, and
re-install the MBR with the command: /sbin/lilo.
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
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
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
Essentially, you need to follow these steps when you install a new
* Before building the new kernel, make a record with the lsmod
command of the module dependencies that your system currently
uses. For example, part of the lsmod output might look like this:
Module Pages Used by
memory_cs 2 0
ds 2 [memory_cs] 3
i82365 4 2
pcmcia_core 8 [memory_cs ds i82365] 3
sg 1 0
bsd_comp 1 0
ppp 5 [bsd_comp] 0
slhc 2 [ppp] 0
serial 8 0
psaux 1 0
lp 2 0
This tells you for example that the memory_cs module needs the ds
and pcmcia_core modules loaded first. What it doesn't say is that,
in order to avoid recalculating the module dependencies, you may
also need to have the serial, lp, psaux, and other standard
modules available to prevent errors when installing the pcmcia
routines at boot time with insmod. A glance at the /etc/modules
file will tell you what modules the system currently loads, and in
what order. Save a copy of this file for future reference, until
you have successfully installed the new kernel's modules. Also
save the lsmod output to a file, for example, with the command:
* Build the new kernel, and install the boot image, either zImage or
bzImage, to a floppy diskette. To do this, change to the
arch/i386/boot directory (substitute the correct architecture
directory if you don't have an Intel machine), and, with a floppy
in the diskette drive, execute the command:
$ dd if=bzImage of=/dev/fd0 bs=512
if you built the kernel with the make bzImage command, and if your
floppy drive is /dev/fd0. This results in a bootable kernel image
being written to the floppy, and allows you to try out the new
kernel without replacing the existing one that LILO boots on the
* Boot the new kernel from the floppy to make sure that it works.
* With the system running the new kernel, compile and install a
current version of the PCMCIA Card Services package, available
from metalab.unc.edu as well as other Linux archives. Before
installing the Card Services utilities, change the names of
/sbin/cardmgr and /sbin/cardctl to /sbin/cardmgr.old and
/sbin/cardctl.old. The old versions of these utilities are not
compatible with the replacement utilities that Card Services
installs. In case something goes awry with the installation, the
old utilities won't be overwritten, and you can revert to the
older versions if necessary. When configuring Card Services with
the "make config" command, make sure that the build scripts know
where to locate the kernel configuration, either by using
information from the running kernel, or telling the build process
where the source tree of the new kernel is. The "make config" step
should complete without errors. Installing the modules from the
Card Services package places them in the directory
/lib/modules/version/pcmcia, where version is the version number
of the new kernel.
* Reboot the system, and note which, if any, of the PCMCIA devices
work. Also make sure that the non-PCMCIA hardware devices are
working. It's likely that some or all of them won't work. Use
lsmod to determine which modules the kernel loaded at boot time,
and compare it with the module listing that the old kernel loaded,
which you saved from the first step of the procedure. (If you
didn't save a listing of the lsmod output, go back and reboot the
old kernel, and make the listing now.)
* When all modules are properly loaded, you can replace the old
kernel image on the hard drive. This will most likely be the file
pointed to by the /vmlinuz symlink. Remember to update the boot
sector by running the lilo command after installing the new kernel
image on the hard drive.
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.
7. How To Do This or Find Out That...
7.1. How To Find Out If a Notebook Runs Linux.
There's no fixed answer to this question, because notebook hardware is
constantly updated, and getting the X display, sound, PCMCIA, modem,
and so forth, working, can take a good deal of effort.
Most notebooks currently on the market, for example, use "Winmodems,"
which often do not work with Linux because of their proprietary
hardware interfaces. Even notebooks which are certified as "Linux
compatible," may not be completely compatible.
Information about installing Winmodems in general is contained in the
Winmodems-and-Linux HOWTO. (Refer to "Where Is the Documentation?")
You can find the most current information, or ask other users about
their notebook experiences, on the linux-laptop mailing list, which is
hosted by the vger.redhat.com server. (Refer to "What Mailing Lists
A mailing list for Linux on IBM Thinkpads has its home page at
Another Thinkpad mailing list is hosted by http://www.bm-soft.com/.
Send email with the word "help" in the body of the message to
There is a Web page about Linux on IBM Thinkpads at
The Linux Laptop home page is at
For information about interfacing peripherals like Zip and CD-ROM
drives through parallel ports, refer to the Linux Parallel Port Home
Page, at http://www.torque.net/linux-pp.html.
If you need the latest version of the PCMCIA Card Services package, it
is (or was) located at ftp://cb-iris.stanford.edu/pub/pcmcia/, but
that host no longer seems to be available. Recent distributions are on
ftp://metalab.unc.edu/pub/Linux/kernel/pcmcia/. You will also need to
have the kernel source code installed as well. Be sure to read the
PCMCIA-HOWTO, which is included in the distribution.
7.2. Installing Linux Using FTP.
Most distributions are too large and complex to make FTP installation
practical. Installing a basic Linux system that doesn't have a GUI or
major applications is possible with FTP, however. The main
non-commercial distribution in use is Debian GNU/Linux, and this
answer describes an installation of a basic Debian system, to which
you can add other Linux applications and commercial software as
This answer describes installation on IBM-compatible machines with an
Intel x86 or Pentium processor. You will need a machine with at least
a 80386 processor, 8 Mb of memory, and about 100 Mb of disk space.
More memory and a larger disk is necessary however, for practical
For other hardware, substitute "-arm," "-ppc," "-m68k," or other
abbreviation in directory names for "-i386."
For detailed and hardware-specific information refer to:
* Connect using anonymous FTP to ftp.debian.org and cd to the
* Retrieve the binary image files for the rescue disk, and the
drivers disk. Depending on the floppy drive installed on your
machine, retrieve either the diskette images with "1200" in the
names if you have a 1.2 Mb, 5.25-in. floppy, or the disks with
"1440" in the name if the computer has a 3.25-in., 1.44 Mb floppy.
Then retrieve the base system diskettes. Note that there are 7
base system images in the 1.44-Mb set (which have a "14" in their
names) , and 9 in the 1.2-Mb set of images (which have a "12" in
their names). You will use these to create the basic installation
diskettes. If you have a Linux machine, you can use dd to write
the images to the diskettes. If you are creating the installation
diskettes on a MS-DOS machine, also download the RAWRITE.EXE
MS-DOS utility, which will copy the raw binary images to floppy
disks. Also download the install.en.txt document, which contains
the detailed installation instructions.
* Create the installation disk set on floppies using either dd under
Linux (e.g.: "dd if=resc1440.bin of=/dev/fd0"), or the RAWRITE.EXE
utility under MS-DOS. Be sure to label each installation diskette.
* Insert the rescue diskette into the floppy drive and reboot the
computer. If all goes well, the Linux kernel will boot, and you
will be able start the installation program by pressing Enter at
the boot: prompt.
* Follow the on-screen instructions for partitioning the hard disk,
installing device drivers, the basic system software, and the
Linux kernel. If the machine is connected to a local network,
enter the network information when the system asks for it.
* To install additional software over the Internet, be sure that you
have installed the ppp module during the installation process, and
run (as root) the /usr/sbin/pppconfig utility. You will need to
provide your user name with your ISP, your password, the ISP's
dial-up phone number, the address(es) of the ISP's Domain Name
Service, and the serial port that your modem is connected to,
/dev/ttyS0-/dev/ttyS3. Be sure also to specify the defaultroute
option to the PPP system, so the computer knows to use the PPP
connection for remote Internet addresses.
* You may have to perform additional configuration on the PPP
scripts in the /etc/ppp subdirectory, and in particular, the
ISP-specific script in the /etc/ppp/peers subdirectory. There are
basic instructions in each script. For detailed information, refer
to the Debian/GNU Linux installation instructions that you
downloaded, the pppd manual page (type man pppd), and the PPP
HOWTO from the Linux Documentation project,
* Once you have a PPP connection established with your ISP (it will
be displayed in the output of ifconfig), use the dselect program
to specify which additional software you want to install. Use the
apt [A]ccess option to retrieve packages via anonymous FTP, and
make sure to use the [U]pdate option to retrieve a current list of
packages from the FTP archive.
7.3. Resuming an Interrupted Download.
You can use the "reget" command of the standard ftp client program
after reconnecting to pick up where you left off.
Clients like ncftp support resumed FTP downloads, and wget supports
resumed FTP and HTTP downloads.
7.4. Boot-Time Configuration.
You can configure Linux at the lilo: prompt either by typing the
kernel arguments at the BOOT lilo: prompt, or by adding an "append="
directive to the /etc/lilo.conf file; for example:
# At the LILO prompt (example only):
BOOT lilo: parport=0x3bc,7 parport=0x3bc,none serial=0x3f8,4 serial=0x2f8,3
# Example statement for /etc/lilo.conf:
append="parport=0x3bc,none serial=0x3f8,4 serial=0x2f8,3"
If you modify the /etc/lilo.conf file, be sure to run the lilo command
to install the new configuration.
Configuration notes for specific hardware devices are in the
documentation of the kernel source distribution,
/usr/src/linux/Documentation in most distributions.
Refer to the lilo and /etc/lilo.conf manual pages, as well as the LDP
BootPrompt-HowTo ("Where Is the Documentation?"), and the
documentation in /usr/doc/lilo.
7.5. Formatting Man Pages without man or groff.
The man2html program translates groff text to HTML, which you can view
with a Web browser. The man2html program, and many like it, are
availble on the Web. Look for them with your favorite search engine.
The unformatted manual pages are stored in subdirectories of /usr/man,
/usr/local/man, and elsewhere.
If you want to view text, use nroff and less. Both of these programs
have MSDOS versions with an implementation of the man macro package
available as well. An example would be:
$ nroff -man /usr/man/man1/ls.1 | less
If you know where to find a good implementation of the man macros
without installing groff, please let the FAQ maintainer know.
If the manual page filename ends in ".gz," then you'll need to
uncompress it before formatting it, using gzip -d or gunzip. A
one-line example would be:
$ gzip -dc /usr/man/man1/ls.1.gz | nroff -man | less
7.6. How To Scroll Backwards in Text Mode.
With the default US keymap, you can use Shift with the PgUp and PgDn
keys. (The gray ones, not the ones on the numeric keypad.) With other
keymaps, look in /usr/lib/keytables. You can remap the ScrollUp and
ScrollDown keys to be whatever you like.
The screen program,
http://vector.co.jp/vpack/browse/person/an010455.html provides a
searchable scrollback buffer and the ability to take "snapshots" of
Recent kernels that have the VGA Console driver can use dramatically
more memory for scrollback, provided that the video card can actually
handle 64 kb of video memory. Add the line:
to the start of the file drivers/video/vgacon.c. This feature may
become a standard setting in future kernels. If the video frame buffer
is also enabled in the kernel, this setting may not affect buffering.
In older kernels, the amount of scrollback is fixed, because it is
implemented using the video memory to store the scrollback text. You
may be able to get more scrollback in each virtual console by reducing
the total number of VC's. See linux/tty.h.
7.7. How To Get Email to Work.
For sending mail via SMTP (Simple Mail Transfer Protocol) and
receiving mail from an ISP's POP (Post Office Protocol) server, you
can use a desktop client like Netscape Communicator or KDE kmail. You
will need to enter the names of the SMTP and POP servers in the
preferences of the respective application, as well as your E-mail
address (username@isp's-domain-name), and your dial-up password. The
same applies to Usenet News. Enter the name of the NNTP (Network News
Transfer Protocol) server in your News client's preferences section.
You may also have to provide the IP addresses of the ISP's primary and
secondary name servers.
If you have a traditional MTA (Mail Transport Agent) like Sendmail,
Smail, qmail, or Exim, you'll need to follow the instructions in each
package. Basically, configuration entails determining which host
machine, either on your local LAN or via dial-up Internet, is the
"Smart Host," if you're using SMTP. If you're using the older UUCP
protocol, then you'll need to consult the directions for configuring
UUCP, and also make sure that your ISP's system is configured to relay
mail to you.
Information about Internet hosting, and News and E-mail in general, is
available on the Usenet News group news.announce.newusers, and those
FAQ's are also archived at ftp://rtfm.mit.edu/pub/usenet/.
7.8. Sendmail Pauses for Up to a Minute at Each Command.
Make sure that Sendmail can resolve your hostname to a valid (i.e.,
parsable) domain address. If you are not connected to the Internet, or
have a dial-up connection with dynamic IP addressing, add the fully
qualified domain name to the /etc/hosts file, in addition to the base
host name; e.g., if the host name is "bilbo" and the domain is
192.168.0.1 bilbo.bag-end.com bilbo
And make sure that either the /etc/host.conf or /etc/resolv.conf file
contains the line:
Caution: Do not change the "localhost" entry in /etc/hosts, because
many programs depend on it for internal message-passing.
Sendmail takes many factors into account when resolving domain
addresses. These factors, collectively, are known as, "rulesets," in
sendmail jargon. The program does not require that a domain address be
canonical, or even appear to be canonical. In the example above,
"bilbo." (note the period) would work just as well as
"bilbo.bag-end.com." This and other modifications apply mainly to
Prior to version 8.7, sendmail required that the FQDN appear first in
the /etc/hosts entry. This is due to changes in the envelope address
masquerade options. Consult the sendmail documents.
If you have a domain name server for only a local subnet, make sure
that "." refers to a SOA record on the server machine, and that
reverse lookups (check by using nslookup) work for all machines on the
Finally, FEATURE configuration macro options like nodns,
always_add_domain, and nocanonify, control how sendmail interprets
The document, Sendmail: Installation and Operation Guide, included in
the doc/ subdirectory of Sendmail source code distributions, discusses
briefly how Sendmail resolves Internet addresses. Sendmail source code
archives are listed at: http://www.sendmail.org/
7.9. How To Enable and Select Virtual Consoles.
In text mode, press the left Alt-F1 to Alt-F12 to select the consoles
tty1 to tty12; Right Alt-F1 gives tty13 and so on. To switch out of X
you must press Ctrl-Alt-F1, etc; Alt-F5 or whatever will switch back.
However, If you have a non-PC compatible system, please see the note
If you want to use a VC for ordinary login, it must be listed in
/etc/inittab, which controls which terminals and virtual consoles have
login prompts. The X Window System needs at least one free VC in order
[Note: The key sequence is actually Ctrl--Meta-- FN. On PC compatible
systems, the right and left Alt keys are really synonymous with the
keysymbols Meta_L and Meta_R. If the binding is different, you can
determine what keys produce Meta_L and Meta_R with xkeycaps or a
7.10. How To Set the Time Zone.
Change directory to /usr/lib/zoneinfo/. Get the time zone package if
you don't have this directory. The source is available in
Then make a symbolic link named localtime pointing to one of the files
in this directory (or a subdirectory), and one called posixrules
pointing to localtime. For example:
$ ln -sf US/Mountain localtime
$ ln -sf localtime posixrules
This change will take effect immediately--try date.