24 Special System Features #
This chapter starts with information about various software packages, the
virtual consoles and the keyboard layout. We talk about software components
like bash
,
cron
and
logrotate
, because they were
changed or enhanced during the last release cycles. Even if they are small
or considered of minor importance, users should change their default
behavior, because these components are often closely coupled with the
system. The chapter concludes with a section about language and
country-specific settings (I18N and L10N).
24.1 Information about Special Software Packages #
The programs bash
,
cron
,
logrotate
,
locate
,
ulimit
and
free
are very important for system
administrators and many users. Man pages and info pages are two useful
sources of information about commands, but both are not always available. GNU
Emacs is a popular and very configurable text editor.
24.1.1 The bash
Package and /etc/profile
#
Bash is the default system shell. When used as a login shell, it reads several initialization files. Bash processes them in the order they appear in this list:
/etc/profile
~/.profile
/etc/bash.bashrc
~/.bashrc
Make custom settings in ~/.profile
or
~/.bashrc
. To ensure the correct processing of these
files, it is necessary to copy the basic settings from
/etc/skel/.profile
or
/etc/skel/.bashrc
into the home directory of the user.
It is recommended to copy the settings from /etc/skel
after an update. Execute the following shell commands to prevent the loss of
personal adjustments:
mv ~/.bashrc ~/.bashrc.old cp /etc/skel/.bashrc ~/.bashrc mv ~/.profile ~/.profile.old cp /etc/skel/.profile ~/.profile
Then copy personal adjustments back from the *.old
files.
24.1.2 The cron Package #
Use cron to run commands automatically in the background at predefined times. cron uses specially formatted time tables, and the tool comes with several default ones. Users can also specify custom tables, if needed.
The cron tables are located in /var/spool/cron/tabs
.
/etc/crontab
serves as a systemwide cron table. Enter
the user name to run the command directly after the time table and before
the command. In Example 24.1, “Entry in /etc/crontab”,
root
is entered. Package-specific
tables, located in /etc/cron.d
, have the same format.
See the cron
man page (man cron
).
1-59/5 * * * * root test -x /usr/sbin/atrun && /usr/sbin/atrun
You cannot edit /etc/crontab
by calling the command
crontab -e
. This file must be loaded directly into an
editor, then modified and saved.
A number of packages install shell scripts to the directories
/etc/cron.hourly
, /etc/cron.daily
,
/etc/cron.weekly
and
/etc/cron.monthly
, whose execution is controlled by
/usr/lib/cron/run-crons
.
/usr/lib/cron/run-crons
is run every 15 minutes from
the main table (/etc/crontab
). This guarantees that
processes that may have been neglected can be run at the proper time.
To run the hourly
, daily
or other
periodic maintenance scripts at custom times, remove the time stamp files
regularly using /etc/crontab
entries (see
Example 24.2, “/etc/crontab: Remove Time Stamp Files”, which removes the
hourly
one before every full hour, the
daily
one once a day at 2:14 a.m., etc.).
59 * * * * root rm -f /var/spool/cron/lastrun/cron.hourly 14 2 * * * root rm -f /var/spool/cron/lastrun/cron.daily 29 2 * * 6 root rm -f /var/spool/cron/lastrun/cron.weekly 44 2 1 * * root rm -f /var/spool/cron/lastrun/cron.monthly
Or you can set DAILY_TIME
in
/etc/sysconfig/cron
to the time at which
cron.daily
should start. The setting of
MAX_NOT_RUN
ensures that the daily tasks get triggered to
run, even if the user did not turn on the computer at the specified
DAILY_TIME
for a longer time. The maximum value of
MAX_NOT_RUN
is 14 days.
The daily system maintenance jobs are distributed to various scripts for
reasons of clarity. They are contained in the package
aaa_base-extras
.
/etc/cron.daily
contains, for example, the components
suse.de-backup-rpmdb
and
suse.de-cron-local
.
24.1.3 Stopping Cron Status Messages #
To avoid the mail-flood caused by cron status messages, the default value of
SEND_MAIL_ON_NO_ERROR
in
/etc/sysconfig/cron
is set to "no
"
for new installations. Even with this setting to "no
",
cron data output will still be sent to the MAILTO
address, as documented in the cron man page.
In the update case it is recommended to set these values according to your needs.
24.1.4 Log Files: Package logrotate #
There are several system services (daemons) that, along
with the kernel itself, regularly record the system status and specific
events onto log files. This way, the administrator can regularly check the
status of the system at a certain point in time, recognize errors or faulty
functions and troubleshoot them with pinpoint precision. These log files are
normally stored in /var/log
as specified by FHS and grow
on a daily basis. The logrotate
package helps
control the growth of these files. For more details refer to Section 3.3, “Managing Log Files with logrotate
”.
24.1.5 The locate Command #
locate
, a command for quickly finding files, is not
included in the standard scope of installed software. If desired, install
the package mlocate
, the successor of the package
findutils-locate
. The updatedb process is started
automatically every night or about 15 minutes after booting the system.
24.1.6 The ulimit Command #
With the ulimit
(user limits)
command, it is possible to set limits for the use of system resources and to
have these displayed. ulimit
is especially useful for
limiting available memory for applications. With this, an application can be
prevented from co-opting too much of the system resources and slowing or
even hanging up the operating system.
ulimit
can be used with various options. To limit memory
usage, use the options listed in Table 24.1, “ulimit
: Setting Resources for the User”.
ulimit
: Setting Resources for the User #
|
The maximum resident set size |
|
The maximum amount of virtual memory available to the shell |
|
The maximum size of the stack |
|
The maximum size of core files created |
|
All current limits are reported |
Systemwide default entries are set in /etc/profile
.
Editing this file directly is not recommended, because changes will be
overwritten during system upgrades. To customize systemwide profile
settings, use /etc/profile.local
. Per-user settings
should be made in
~USER/.bashrc
.
# Limits maximum resident set size (physical memory): ulimit -m 98304 # Limits of virtual memory: ulimit -v 98304
Memory allocations must be specified in KB. For more detailed information,
see man bash
.
ulimit
Support
Not all shells support ulimit
directives. PAM (for
example, pam_limits
) offers comprehensive adjustment
possibilities as an alternative to ulimit
.
24.1.7 The free Command #
The free
command displays the total amount of free and
used physical memory as well as swap space in the system and the buffers and
cache consumed by the kernel. The concept of available
RAM dates back to before the days of unified memory management.
The slogan free memory is bad memory applies well to
Linux. As a result, Linux has always made the effort to balance out caches
without actually allowing free or unused memory.
The kernel does not have direct knowledge of any applications or user data.
Instead, it manages applications and user data in a page
cache. If memory runs short, parts of it are written to the swap
partition or to files, from which they can initially be read using the mmap
command (see man mmap
).
The kernel also contains other caches, such as the slab
cache, where the caches used for network access are stored. This
may explain the differences between the counters in
/proc/meminfo
. Most, but not all, of them can be
accessed via /proc/slabinfo
.
However, if your goal is to find out how much RAM is currently being used,
find this information in /proc/meminfo
.
24.1.8 Man Pages and Info Pages #
For some GNU applications (such as tar), the man pages are no longer
maintained. For these commands, use the --help
option to
get a quick overview of the info pages, which provide more in-depth
instructions. Info
is GNU's hypertext system. Read an introduction to this system by entering
info
info
. Info pages can be viewed with
Emacs by entering emacs
-f info
or
directly in a console with info
. You can also use tkinfo,
xinfo or the help system to view info pages.
24.1.9 Selecting Man Pages Using the man
Command #
To read a man page enter man
MAN_PAGE. If a man page with the same name exists
in different sections, they will all be listed with the corresponding
section numbers. Select the one to display. If you do not enter a section
number within a few seconds, the first man page will be displayed.
To change this to the default system behavior, set
MAN_POSIXLY_CORRECT=1
in a shell initialization file such
as ~/.bashrc
.
24.1.10 Settings for GNU Emacs #
GNU Emacs is a complex work environment. The following sections cover the configuration files processed when GNU Emacs is started. More information is available at http://www.gnu.org/software/emacs/.
On start-up, Emacs reads several files containing the settings of the user,
system administrator and distributor for customization or preconfiguration.
The initialization file ~/.emacs
is installed to the
home directories of the individual users from /etc/skel
.
.emacs
, in turn, reads the file
/etc/skel/.gnu-emacs
. To customize the program, copy
.gnu-emacs
to the home directory (with cp
/etc/skel/.gnu-emacs ~/.gnu-emacs
) and make the desired settings
there.
.gnu-emacs
defines the file
~/.gnu-emacs-custom
as custom-file
.
If users make settings with the customize
options in
Emacs, the settings are saved to ~/.gnu-emacs-custom
.
With SUSE Linux Enterprise Server, the emacs
package installs the file site-start.el
in the directory
/usr/share/emacs/site-lisp
. The file
site-start.el
is loaded before the initialization file
~/.emacs
. Among other things,
site-start.el
ensures that special configuration files
distributed with Emacs add-on packages, such as
psgml
, are loaded automatically.
Configuration files of this type are located in
/usr/share/emacs/site-lisp
, too, and always begin with
suse-start-
. The local system administrator can specify
systemwide settings in default.el
.
More information about these files is available in the Emacs info file under
Init File: info:/emacs/InitFile
.
Information about how to disable the loading of these files (if necessary) is
also provided at this location.
The components of Emacs are divided into several packages:
The base package
emacs
.emacs-x11
(usually installed): the program with X11 support.emacs-nox
: the program without X11 support.emacs-info
: online documentation in info format.emacs-el
: the uncompiled library files in Emacs Lisp. These are not required at runtime.Numerous add-on packages can be installed if needed:
emacs-auctex
(LaTeX),psgml
(SGML and XML),gnuserv
(client and server operation) and others.
24.2 Virtual Consoles #
Linux is a multiuser and multitasking system. The advantages of these features can be appreciated even on a stand-alone PC system. In text mode, there are six virtual consoles available. Switch between them using Alt–F1 through Alt–F6. The seventh console is reserved for X and the tenth console shows kernel messages.
To switch to a console from X without shutting it down, use Ctrl–Alt–F1 to Ctrl–Alt–F6. To return to X, press Alt–F7.
24.3 Keyboard Mapping #
To standardize the keyboard mapping of programs, changes were made to the following files:
/etc/inputrc /etc/X11/Xmodmap /etc/skel/.emacs /etc/skel/.gnu-emacs /etc/skel/.vimrc /etc/csh.cshrc /etc/termcap /usr/share/terminfo/x/xterm /usr/share/X11/app-defaults/XTerm /usr/share/emacs/VERSION/site-lisp/term/*.el
These changes only affect applications that use terminfo
entries or whose configuration files are changed directly
(vi
, emacs
, etc.). Applications not
shipped with the system should be adapted to these defaults.
Under X, the compose key (multikey) can be enabled as explained in
/etc/X11/Xmodmap
.
Further settings are possible using the X Keyboard Extension (XKB). This extension is also used by the desktop environment GNOME (gswitchit).
Information about XKB is available in the documents listed in
/usr/share/doc/packages/xkeyboard-config
(part of the
xkeyboard-config
package).
24.4 Language and Country-Specific Settings #
The system is, to a very large extent, internationalized and can be modified for local needs. Internationalization (I18N) allows specific localization (L10N). The abbreviations I18N and L10N are derived from the first and last letters of the words and, in between, the number of letters omitted.
Settings are made with LC_
variables defined in the
file /etc/sysconfig/language
. This refers not only to
native language support, but also to the categories
Messages (Language), Character Set,
Sort Order, Time and Date,
Numbers and Money. Each of these
categories can be defined directly with its own variable or indirectly with a
master variable in the file language
(see the
locale
man page).
RC_LC_MESSAGES
,RC_LC_CTYPE
,RC_LC_COLLATE
,RC_LC_TIME
,RC_LC_NUMERIC
,RC_LC_MONETARY
These variables are passed to the shell without the
RC_
prefix and represent the listed categories. The shell profiles concerned are listed below. The current setting can be shown with the commandlocale
.RC_LC_ALL
This variable, if set, overwrites the values of the variables already mentioned.
RC_LANG
If none of the previous variables are set, this is the fallback. By default, only
RC_LANG
is set. This makes it easier for users to enter their own values.ROOT_USES_LANG
A
yes
orno
variable. If set tono
,root
always works in the POSIX environment.
The variables can be set with the YaST sysconfig editor. The value of such a variable contains the language code, country code, encoding and modifier. The individual components are connected by special characters:
LANG=<language>[[_<COUNTRY>].<Encoding>[@<Modifier>]]
24.4.1 Some Examples #
You should always set the language and country codes together. Language settings follow the standard ISO 639 available at http://www.evertype.com/standards/iso639/iso639-en.html and http://www.loc.gov/standards/iso639-2/. Country codes are listed in ISO 3166, see http://en.wikipedia.org/wiki/ISO_3166.
It only makes sense to set values for which usable description files can be
found in /usr/lib/locale
. Additional description files
can be created from the files in /usr/share/i18n
using
the command localedef
. The description files are part of
the glibc-i18ndata
package. A description file for
en_US.UTF-8
(for English and United States) can be
created with:
localedef -i en_US -f UTF-8 en_US.UTF-8
-
LANG=en_US.UTF-8
This is the default setting if American English is selected during installation. If you selected another language, that language is enabled but still with UTF-8 as the character encoding.
-
LANG=en_US.ISO-8859-1
This sets the language to English, country to United States and the character set to
ISO-8859-1
. This character set does not support the Euro sign, but it can be useful sometimes for programs that have not been updated to supportUTF-8
. The string defining the charset (ISO-8859-1
in this case) is then evaluated by programs like Emacs.LANG=en_IE@euro
The above example explicitly includes the Euro sign in a language setting. This setting is obsolete now, as UTF-8 also covers the Euro symbol. It is only useful if an application supports ISO-8859-15 and not UTF-8.
Changes to /etc/sysconfig/language
are activated by the
following process chain:
For the Bash:
/etc/profile
reads/etc/profile.d/lang.sh
which, in turn, analyzes/etc/sysconfig/language
.For tcsh: At login,
/etc/csh.login
reads/etc/profile.d/lang.csh
which, in turn, analyzes/etc/sysconfig/language
.
This ensures that any changes to
/etc/sysconfig/language
are available at the next login
to the respective shell, without having to manually activate
them.
Users can override the system defaults by editing their
~/.bashrc
accordingly. For example, if you do not want
to use the system-wide en_US
for program messages,
include LC_MESSAGES=es_ES
so that messages are
displayed in Spanish instead.
24.4.2 Locale Settings in ~/.i18n
#
If you are not satisfied with locale system defaults, change the settings in
~/.i18n
according to the Bash scripting syntax. Entries
in ~/.i18n
override system defaults from
/etc/sysconfig/language
. Use the same variable names
but without the RC_
name space prefixes. For example, use
LANG
instead of RC_LANG
:
LANG=cs_CZ.UTF-8 LC_COLLATE=C
24.4.3 Settings for Language Support #
Files in the category Messages are, as a rule, only
stored in the corresponding language directory (like
en
) to have a fallback. If you set
LANG
to en_US
and the message
file in /usr/share/locale/en_US/LC_MESSAGES
does not
exist, it falls back to
/usr/share/locale/en/LC_MESSAGES
.
A fallback chain can also be defined, for example, for Breton to French or for Galician to Spanish to Portuguese:
LANGUAGE="br_FR:fr_FR"
LANGUAGE="gl_ES:es_ES:pt_PT"
If desired, use the Norwegian variants Nynorsk and Bokmål instead (with
additional fallback to no
):
LANG="nn_NO"
LANGUAGE="nn_NO:nb_NO:no"
or
LANG="nb_NO"
LANGUAGE="nb_NO:nn_NO:no"
Note that in Norwegian, LC_TIME
is also treated
differently.
One problem that can arise is a separator used to delimit groups of digits
not being recognized properly. This occurs if LANG
is set to only a two-letter language code like de
, but
the definition file glibc uses is located in
/usr/share/lib/de_DE/LC_NUMERIC
. Thus
LC_NUMERIC
must be set to de_DE
to make the separator definition visible to the system.
24.4.4 For More Information #
The GNU C Library Reference Manual, Chapter “Locales and Internationalization”. It is included in
glibc-info
. The package is available from the SUSE Linux Enterprise SDK. The SDK is a module for SUSE Linux Enterprise and is available via an online channel from the SUSE Customer Center. Alternatively, go to http://download.suse.com/, search forSUSE Linux Enterprise Software Development Kit
and download it from there. Refer to Capitolo 14, Installazione di moduli, estensioni e prodotti aggiuntivi di terze parti for details.Markus Kuhn, UTF-8 and Unicode FAQ for Unix/Linux, currently at https://www.cl.cam.ac.uk/~mgk25/unicode.html.
Unicode-HOWTO by Bruno Haible, available at http://tldp.org/HOWTO/Unicode-HOWTO-1.html.