Show Lecture.Config as a slide show.
CT320 Config
Smash Cut
- A smash cut is a technique used in visual media:
film, TV, comics, etc.
- In one version, a character firmly declares that something will
not happen, or asks a ludicrous rhetorical question,
followed immediately by that thing happening.
- This version is sometimes known as the Gilligan Cut, due to its
use in the television show Gilligan’s Island.
blix
Consider the blix command (I made it up), which blixes things.
It requires configuration information.
- What things should be blixed?
- How often should the blixing take place?
- If this high- or low-priority blixing?
- Which uses are permitted to blix?
- What is the default blixing level?
A configuration file
The straightforward solution is to have a configuration file,
/etc/blix.conf. It’s installed as part of the blix package,
and contains default values, such as:
Frequency: 30m # Every 30 minutes
Priority: medium
Level: 3 # 1 is lowest level, 5 is highest level
Users: root # Only root is permitted to blix
To allow user sanchez to blix, change the last line to:
Users: root,sanchez # Sanchez, too!
Problem
What happens when a new revision of the blix package comes out?
A new parameter has been added to /etc/blix.conf. However,
you’ve edited /etc/blix.conf:
| Old
| New
|
|---|
Frequency: 30m
Priority: medium
Level: 3
Users: root,sanchez
|
Frequency: 30m
Priority: medium
Level: 3
Users: root
Compression: xz
|
Conflict! When you update, you’ll have to merge that file manually.
Ack!
Solution #1
You could have separate system & user config files:
/etc/blix.system.conf
/etc/blix.user.conf
/etc/blix.system.conf would be reserved for the system defaults,
and /etc/blix.user.conf would be available for user editing.
That sounds great, but …
Problem
What if another package wants to add some blixing information?
Say that the vim package wants to add a line to the blix
configuration file to specify how often ~/.vimrc should be blixed?
Whichever file it modifies, we’ll have the same old problem at the
next update.
What are we supposed to do—have an unlimited number of configuration
files!?
An Unlimited Number of Configuration Files
(That’s a smash cut, you see.)
- Bad:
/etc/blix.conf
- Better:
/etc/blix.system.conf & /etc/blix.user.conf
- Best:
/etc/blix.d/*
Instead of a single configuration file /etc/blix.conf, or just a few
config files, have a directory /etc/blix.d.
The blix program will treat all files in /etc/blix.d as
configuration file.
Forcing Order
If the order matters, we can add prefixes
to the filenames to force processing order:
/etc/blix.d/40-vim (via the vim package)
/etc/blix.d/50-blix (defaults provided via the blix package)
/etc/blix.d/90-user (created by the user)
The filenames will be unique, as long as two packages don’t use
the same name.
It’s Popular
$ ls -ld /etc/*.d
drwxr-xr-x. 2 root root 4096 Dec 5 2019 /etc/ant.d
drwxr-xr-x. 2 root root 4096 Oct 14 2023 /etc/auto.master.d
drwxr-xr-x. 2 root root 4096 Apr 12 11:42 /etc/bash_completion.d
drwxr-xr-x. 2 root root 4096 Oct 15 2023 /etc/binfmt.d
drwxr-xr-x. 2 root root 4096 Oct 14 2023 /etc/chkconfig.d
drwxr-xr-x. 2 root root 4096 Mar 6 09:37 /etc/cron.d
drwxr-xr-x. 2 root root 4096 Dec 19 09:30 /etc/depmod.d
drwxr-xr-x. 2 root dnsmasq 4096 Mar 14 14:05 /etc/dnsmasq.d
drwxr-xr-x. 2 root root 4096 Oct 14 2023 /etc/dracut.conf.d
drwxr-xr-x. 2 root root 4096 Mar 31 2023 /etc/exports.d
drwxr-xr-x. 2 root root 4096 Apr 12 11:41 /etc/gdbinit.d
drwx------. 2 root root 4096 Apr 12 11:42 /etc/grub.d
lrwxrwxrwx 1 root root 11 Oct 14 2023 /etc/init.d -> rc.d/init.d
drwx------. 3 root root 4096 Oct 11 2023 /etc/ipsec.d
drwxr-xr-x. 2 root root 4096 Sep 7 2021 /etc/issue.d
drwxr-xr-x. 2 root root 4096 Nov 15 00:47 /etc/krb5.conf.d
drwxr-xr-x. 2 root root 4096 Apr 12 12:33 /etc/ld.so.conf.d
drwxr-xr-x. 2 root root 4096 Dec 19 09:24 /etc/libibverbs.d
drwxr-xr-x. 2 root root 4096 Oct 12 2019 /etc/libpaper.d
drwxr-xr-x. 2 root root 4096 Nov 23 01:15 /etc/logrotate.d
drwxr-xr-x. 2 root root 4096 Sep 7 2021 /etc/lsb-release.d
drwxr-xr-x 3 root root 4096 Apr 18 2022 /etc/mdevctl.d
drwxr-xr-x. 2 root root 4096 Oct 14 2023 /etc/modprobe.d
drwxr-xr-x. 2 root root 4096 Oct 15 2023 /etc/modules-load.d
drwxr-xr-x. 2 root root 4096 Oct 14 2023 /etc/motd.d
drwxr-xr-x. 2 root root 4096 Sep 7 2021 /etc/my.cnf.d
drwxr-xr-x. 2 root root 4096 Apr 1 2023 /etc/oddjobd.conf.d
drwxr-xr-x. 2 root root 4096 Dec 19 09:52 /etc/pam.d
drwxr-xr-x. 2 root root 4096 Jan 4 2022 /etc/php.d
drwxr-xr-x. 2 root root 4096 Sep 7 2021 /etc/php-fpm.d
drwxr-xr-x. 2 root root 4096 Apr 28 2023 /etc/popt.d
drwxr-xr-x. 2 root root 4096 Apr 12 11:41 /etc/prelink.conf.d
drwxr-xr-x. 2 root root 4096 Apr 12 11:42 /etc/profile.d
lrwxrwxrwx 1 root root 10 Oct 14 2023 /etc/rc0.d -> rc.d/rc0.d
lrwxrwxrwx 1 root root 10 Oct 14 2023 /etc/rc1.d -> rc.d/rc1.d
lrwxrwxrwx 1 root root 10 Oct 14 2023 /etc/rc2.d -> rc.d/rc2.d
lrwxrwxrwx 1 root root 10 Oct 14 2023 /etc/rc3.d -> rc.d/rc3.d
lrwxrwxrwx 1 root root 10 Oct 14 2023 /etc/rc4.d -> rc.d/rc4.d
lrwxrwxrwx 1 root root 10 Oct 14 2023 /etc/rc5.d -> rc.d/rc5.d
lrwxrwxrwx 1 root root 10 Oct 14 2023 /etc/rc6.d -> rc.d/rc6.d
drwxr-xr-x. 10 root root 4096 Oct 14 2023 /etc/rc.d
drwxr-xr-x. 2 root root 4096 Apr 18 2022 /etc/reader.conf.d
drwxr-xr-x. 2 root root 4096 Oct 8 2021 /etc/request-key.d
drwxr-xr-x. 2 root root 4096 Oct 14 2023 /etc/rsyslog.d
drwxr-xr-x. 2 root root 4096 Nov 15 08:33 /etc/rwtab.d
drwxr-xr-x. 3 root root 4096 Sep 7 2021 /etc/sane.d
drwxr-xr-x. 2 root root 4096 Nov 9 2022 /etc/sddm.conf.d
drwxr-xr-x. 2 root root 4096 Oct 8 2021 /etc/sensors.d
drwxr-x---. 2 root root 4096 Apr 4 2023 /etc/sudoers.d
drwxr-xr-x. 2 root root 4096 Jul 17 2021 /etc/supervisord.d
drwxr-xr-x. 2 root root 4096 Oct 15 2023 /etc/sysctl.d
drwxr-xr-x. 2 root root 4096 Apr 12 11:42 /etc/tmpfiles.d
drwxr-xr-x. 2 root root 4096 Oct 9 2021 /etc/xinetd.d
drwxr-xr-x. 2 root root 4096 Apr 28 2023 /etc/yum.repos.d
Cron Example
$ ls -l /etc/cron.d
total 8
-rw-r--r--. 1 root root 128 Mar 6 09:37 0hourly
-rw-r--r--. 1 root root 108 Oct 14 2023 raid-check