15. Tips And Tricks

Q: How Do I Format Man Pages without man or groff?
Q: How To Scroll Backwards in Text Mode
Q: How To Get Email to Work
Q: Sendmail Pauses for Up to a Minute at Each Command
Q: How To Enable and Select Virtual Consoles
Q: How To Set the Time Zone
Q: What Is a core File?
Q: How To Enable or Disable Core Dumps
Q: How To Remap a Keyboard to UK, French, Etc.
Q: How To Get NUM LOCK to Default to On
Q: How To Set (Or Reset) Initial Terminal Colors
Q: How To Have More Than 128Mb of Swap

Q: How Do I Format Man Pages without man or groff?

A: 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 

Q: How To Scroll Backwards in Text Mode

A: 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 text-mode screens.

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:

 #define VGA_CAN_DO_64B 

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.

[Chris Karakas]

Q: How To Get Email to Work

A: 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 (e.g., username@example.com), 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/.

Q: Sendmail Pauses for Up to a Minute at Each Command

A: 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 bag-end.com: bilbo.bag-end.com bilbo 

And make sure that either the /etc/host.conf or /etc/resolv.conf file contains the line:

 order hosts,bind 

CautionDo not change the localhostentry 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 recent versions.

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 subnet.

Finally, FEATURE configuration macro options like nodns, always_add_domain, and nocanonify, control how sendmail interprets host names.

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/

[Chris Karakas]

Q: How To Enable and Select Virtual Consoles

A: 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 below.

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 to start.

NoteThe key sequence is actually CtrlMetaFN. On PC compatible systems, the right and left Altkeys are really synonymous with the keysymbols Meta_Land Meta_R. If the binding is different, you can determine what keys produce Meta_Land Meta_Rwith xkeycapsor a similar application.

[David Charlap]

Q: How To Set the Time Zone

A: Change directory to /usr/lib/zoneinfo/. Get the time zone package if you don't have this directory. The source is available in ftp://metalab.unc.edu/pub/Linux/system/admin/time/.

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 immediatelytry date.

If the system uses Red Hat-style configuration files, the respective time zone info files are /usr/share/zoneinfo and /etc/localtime.

The manual pages for tzset or tzselect describe setting the time zone. Some programs recognize the TZ environment variable, but this is not POSIX-correct.

You should also make sure that your Linux kernel clock is set to the correct GMT time. Type date -u and check that the correct UTC time is displayed. See Why Does the Computer Have the Wrong Time?.

Q: What Is a core File?

A: A core file is created when a program terminates unexpectedly, due to a bug, or a violation of the operating system's or hardware's protection mechanisms. The operating system kills the program and creates a core file that programmers can use to figure out what went wrong. It contains a detailed description of the state that the program was in when it died.

If would like to determine what program a core file came from, use the file command, like this:

 $ file core 

That will tell you the name of the program that produced the core dump. You may want to write the maintainer(s) of the program, telling them that their program dumped core.

[Eric Hanchrow]

Q: How To Enable or Disable Core Dumps

A: By using the ulimit command in bash, the limit command in tcsh, or the rlimit command in ksh. See the appropriate manual page for details.

This setting affects all programs run from the shell (directly or indirectly), not the whole system.

If you wish to enable or disable core dumping for all processes by default, you can change the default setting in linux/sched.h. Refer to definition of INIT_TASK, and look also in linux/resource.h.

PAM support optimizes the system's environment, including the amount of memory a user is allowed. In some distributions this parameter is configurable in the /etc/security/limits.conf file. For more information, refer to the Linux Administrator's Security Guide. See Where Is the Documentation?.

Q: How To Remap a Keyboard to UK, French, Etc.

A: For recent kernels, get /pub/Linux/system/Keyboards/kbd-0.90.tar.gz from ftp://metalab.unc.edu/. Make sure you get the appropriate version; you have to use the right keyboard mapping package for your kernel version.

For older kernels you have to edit the top-level kernel Makefile, in /usr/src/linux/.

You may find more helpful information in The Linux Keyboard and Console HOWTO, by Andries Brouwer, at ftp://metalab.unc.edu/pub/Linux/docs/HOWTO/.

Q: How To Get NUM LOCK to Default to On

A: Use the setleds program, for example (in /etc/rc.local or one of the /etc/rc.d/* files):

 for t in 1 2 3 4 5 6 7 8
   setleds +num < /dev/tty$t > /dev/null

setleds is part of the kbd package ("How do I remap my keyboard to UK, French, etc.? ").

Alternatively, patch your kernel. You need to arrange for KBD_DEFLEDS to be defined to (1 << VC_NUMLOCK) when compiling drivers/char/keyboard.c.

Q: How To Set (Or Reset) Initial Terminal Colors

A: The following shell script should work for VGA consoles:

 for n in 1 2 4 5 6 7 8;
   setterm -fore yellow -bold on -back blue -store > /dev/tty$n

Substitute your favorite colors, and use /dev/ttyS$n for serial terminals.

To make sure they are reset when people log out (if they've been changed):

Replace the references to getty (or mingetty or uugetty or whatever) in /etc/inittab with references to /sbin/mygetty.

 #!/bin/sh setterm -fore yellow -bold on -back blue -store > $1
 exec /sbin/mingetty $@

[Jim Dennis]

Q: How To Have More Than 128Mb of Swap

A: Use several swap partitions or swap files. Linux kernels before version 2.2 supported up to 16 swap areas, each of up to 128Mb. Recent versions do not have this limitation.

Very old kernels only supported swap partition sizes up to 16Mb.

Linux on machines with 8KB paging, like Alpha and Sparc64, support a swap partition up to 512MB. The 128MB limitation comes from PAGE_SIZE*BITSPERBYTE on machines with 4KB paging, but is 512KB on machines with 8KB paging. The limit is due to the use of a single page allocation map.

The file mm/swapfile.c has all of the gory details.

[Peter Moulder, Gordon Weast]