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User Journal

Journal: 7 - Why does Gimp depend on systemd? 2

Journal by phantomfive

This post is flotsam related to some dependencies. If you note any mistakes, please let me know, I'm collecting information.

Gimp doesn't depend on systemd as far as I can tell. Gimp runs on Windows. It does depend on libgtk, whose dependency list is available.

There are reports that Gimp depends on systemd, but that seems to be an artifact of a package dependency tree on one system, not that Gimp actually needs systemd.

What about Gnome? Does Gnome depend on systemd? The answer is yes....., although there are alternatives. Systembsd, systemd-shim, and LoginKit.

LoginKit doesn't seem to be complete, like some files were missing from commit or something. The README is attractive, though. It seems to only be attempting to provide services for logind.

Systembsd provides hostenamed, localed, logind, and timedated.

Systemd-shim provides c-group services, some unit file services, power/sleep/reboot services, and ntpdate services.

Neither code base has been updated in four months, and the code in neither one looks particularly well organized.

I suspect there are other things systemd provides that Gnome relies on, but those aren't immediately apparent. I'm not sure where to look to figure that out.

Before logind, Gnome used ConsoleKit to provide login support. Fascinatingly, the commit to remove support for ConsoleKit was made by Florien Mullner.

A lot of this stuff depends directly on DBus. In my opinion that is a mistake; the communication mechanism should be separate from the API interface.

In the next journal entry I will investigate how deeply libsystemd is tied into the init system, or whether it is truly modular.

User Journal

Journal: Systemd (or, how to make portable software) 10

Journal by phantomfive

In this post, Lennart explains that he doesn't know how to write portable C code. He says:

[Making systemd portable] would turn every second line of systemd into #ifdefs.

The purpose of my post here is to explain how to write portable code, without #ifdefs on every other line. If that happens, you are doing it the hard way.

An easier way is to create an OS independent layer. Call it OSI (since no one is using that acronym anymore, right?). Create a header file that declares all your functions, then create an implementation file for each platform. Every time you find a piece of functionality that is different on different platforms, throw it into that header file.

For example, if you need to take a screenshot, it will be different on every platform you find. In the header file, create a function OSI_Screenshot(). Then in your OSI_Windows.c file, add an implementation for windows. In your OSI_Linux.c, add a screenshot implementation for Linux. In your OSI_OSX.c, add your implementation for OSX. This technique can also work for extremely incompatible platforms, with OSI_printf(), or OSI_malloc(), etc. If you use your compiler correctly, you can compile it without any extra overhead from the function call.

An example of this technique can be found in Android (look at sysdeps.h and sysdeps_win32.c), demonstrating that this technique works. They don't have #ifdefs scattered throughout their code. The Android example is tougher than it needs to be, because Android added the compatibility layer after the code was written. If they had started at the beginning, the code would have been much simpler.

The lack of knowledge (about how to write portable code) in the systemd team is causing them to make bad decisions, because the alternative seems too hard. For example:

I have no plans porting it to other kernels, and I will not merge any such patches........Quite frankly, I'd like to question [cross-platform compatibility]. In the light of GNOME OS I think we need to ask ourselves the question if we do ourselves any good if we continue to support all kinds of kernels that simply cannot keep up with Linux anymore.

Those who don't understand the failures of the past are destined to repeat them. Plenty of vendors try to focus on a single platform, and their work disappeared, to be replaced by something that was cross-platform compatible, and usually better work. The discipline required to keep things portable results in better code (there's a quote from Mythical Man Month that fits here but I'm too lazy to look it up). The Gnome developers understand the importance of portability but that's a story for another post.

User Journal

Journal: Systemd's solution to large init scripts 1

Journal by phantomfive

(Note: When you write code, you're making a UI for programmers. Learn to do it well.)

Below you can see a traditional unix init script. It's long, but if you're familiar with shell-script you can figure out what is going on. There is a lot of redundancy here, most init scripts have a switch that runs an option based on the first command-line parameter, for example. One solution is to put common code in a function, but Poettering decided to use config files.

Let's examine the general tradeoff between putting code in a function, and using config files (a form of declarative programming). Config files are fine as long as there aren't too many special cases. If there are too many special cases, you end up with so many options and keywords that it would have been easier to just use a scripting language.

The good side is systemd saves a lot of typing. Way down at the bottom, is a unit file for the same init script. It's clearly shorter, and easier to type.

The bad side is it has arcane keywords which are are not discoverable merely by looking at the file. This is a pattern that repeats itself over and over in systemd, things are easier if you know how to do them, but the system itself is inscrutable without arcane knowledge.

Ideal systems fulfill the requirements while making it easy for those who want to dig deeper. The system opens like the petals of a rose.

#!/bin/bash
# Starts the abrt daemon
#
# chkconfig: 35 82 16
# description: Daemon to detect crashing apps
# processname: abrtd
### BEGIN INIT INFO
# Provides: abrt
# Required-Start: $syslog $local_fs
# Required-Stop: $syslog $local_fs
# Default-Stop: 0 1 2 6
# Default-Start: 3 5
# Short-Description: start and stop abrt daemon
# Description: Listen to and dispatch crash events
### END INIT INFO
 
# Source function library.
. /etc/rc.d/init.d/functions
ABRT_BIN="/usr/sbin/abrtd"
LOCK="/var/lock/subsys/abrtd"
OLD_LOCK="/var/lock/subsys/abrt"
RETVAL=0
 
#
# Set these variables if you are behind proxy
#
#export http_proxy=
#export https_proxy=
 
#
# See how we were called.
#
 
check() {
    # Check that we're a privileged user
    [ "`id -u`" = 0 ] || exit 4
 
    # Check if abrt is executable
    test -x $ABRT_BIN || exit 5
}
 
start() {
 
    check
 
    # Check if it is already running
    if [ ! -f $LOCK ] && [ ! -f $OLD_LOCK ]; then
        echo -n $"Starting abrt daemon: "
        daemon $ABRT_BIN
        RETVAL=$?
        [ $RETVAL -eq 0 ] && touch $LOCK
        echo
    fi
    return $RETVAL
}
 
stop() {
 
    check
 
    echo -n $"Stopping abrt daemon: "
    killproc $ABRT_BIN
    RETVAL=$?
    [ $RETVAL -eq 0 ] && rm -f $LOCK
    [ $RETVAL -eq 0 ] && rm -f $OLD_LOCK
    echo
    return $RETVAL
}
 
restart() {
    stop
    start
}
 
reload() {
    restart
}
 
case "$1" in
start)
    start
;;
stop)
    stop
;;
reload)
    reload
;;
force-reload)
    echo "$0: Unimplemented feature."
    RETVAL=3
;;
restart)
    restart
;;
condrestart)
    if [ -f $LOCK ]; then
        restart
    fi
    # update from older version
    if [ -f $OLD_LOCK ]; then
        restart
    fi
;;
status)
    status abrtd
    RETVAL=$?
;;
*)
    echo $"Usage: $0 {start|stop|status|restart|condrestart|reload|force-reload}"
    RETVAL=2
esac
 
exit $RETVAL

-----------------------------------------------------------------------------------------

[Unit]
Description=Daemon to detect crashing apps
After=syslog.target
 
[Service]
ExecStart=/usr/sbin/abrtd
Type=forking
 
[Install]
WantedBy=multi-user.target

Reference to the examples.

User Journal

Journal: systemd - Why did Debian Adopt it? 8

Journal by phantomfive

There's a Debian debate page, but it's disappointing and everything systemd does is listed with equal value. Thanks to Russ Albery for making a much more balanced assessment, explaining what he likes. The short answer to the question is: SystemD makes things much easier for people writing init scripts. It wasn't about cgroups, or speed, or login managers, it was about writing easy init scripts.

Here are the major complaints he has with the traditional startup system:

* Lack of integration with kernel-level events to properly order startup.
* No mechanism for process monitoring and restarting beyond inittab.
* Heavy reliance on shell scripting rather than declarative syntax.
* A fork and exit with PID file model for daemon startup.

He furthermore points out these problems with startup scripts:

The model of fork and exit without clear synchronization points is inherently racy, the boot model encoded into sysvinit doesn't reflect a modern system boot, and maintaining large and complex init scripts as conffiles has been painful for years. Nearly every init script, including the ones in my own packages, have various edge-case bugs or problems because it's very hard to write robust service startup in shell, even with the excellent helper programs and shell libraries that Debian has available.

Those are the main things that systemd fixes for a distro builder, and probably why so many distros have switched to systemd, because it was built for them.

User Journal

Journal: systemd - A descendent of Apple's LaunchD 1

Journal by phantomfive

Systemd is a descendent of Apple's launchd, Lennart suggested the world watch this movie to learn about it, so why? What is good about launchd?

OSX has an excellent inter-processing message system, part of the mach kernel (which they got from CMU). Because of this, many times processes talk to each other through the standard messaging queues. If you use a library to launch a browser window, or query wifi strength, it will communicate through a message queue (although the library takes care of the details).

The interesting thing is that launchd can open a message queue before the recipient is running. So launchd doesn't launch services until they are needed, and if they aren't needed, they never get launched. The benefit is that resources are preserved, things don't get launched until someone sends a message.

The benefit here is dependency resolution. Instead of forcing a deep calculation of what depends on what, or forcing the server script to declare everything it depends on, you can say "manage all these thousand services!" and only the few that are needed will be used, when they are needed.

Another thing I think Lennart copied from launchd is the declarative config files. You don't need to write a shell script, you merely need to indicate what should be launched, and maybe give it configuration options like "relaunch on failure" or "launch completely before receiving message." Of course, some people like config files, others prefer scripts.....that's not an argument I want to get into here, I'm merely pointing out things that seem to have come from launchd. (

What is bad:

Launchd is utterly undiscoverable. It would have been nice of them to put a README in /etc/rc/ or something saying, "hey, all your startup scripts are gone, look elsewhere."

Launchd has a complex hierarchy of directories that it searches for startup scripts. They have justifications for why, and a reason behind each one.......but justifications and reasons are not the same as good design. Every bad design decision ever made had a justification and a reason.

User Journal

Journal: Systemd - Efficiency and Pike's Rules of Programming 4

Journal by phantomfive

(DISCLAIMER: These are my notes and might be wrong.)

Lennart Poettering has never heard of Rob Pike's rules of programming. Let's examine why:

He said, "On my system the scripts in /etc/init.d call grep at least 77 times.... that has to be incredibly slow...., and should be rewritten in C."

You can time it yourself, with this command:

time for i in {1..77}; do grep user /etc/passwd > /dev/null; done

On my machine it takes 0.229 seconds.

Lennart didn't get the speed increase he wanted. From his benchmark report, "booting up with Upstart takes 27s, with systemd we reach 24s." This result isn't too bad: when I've made a similar mistake of writing code before timing anything, ignoring Pike's rules for programming, once I actually slowed the system down.

If you don't measure, you can't optimize.

For entertainment and enlightenment, here is a quote by Ken Thompson talking vaguely about Pike's rules for programming:

Early Unix programmers became good at modularity because they had to be. An OS is one of the most complicated pieces of code around. If it is not well structured, it will fall apart. There were a couple of early failures at building Unix that were scrapped. One can blame the early (structureless) C for this, but basically it was because the OS was too complicated to write. We needed both refinements in tools (like C structures) and good practice in using them (like Rob Pike's rules for programming) before we could tame that complexity.

User Journal

Journal: SystemD: The Beginning 7

Journal by phantomfive

DISCLAIMER: THIS CODE REVIEW IS A LONG WORK IN PROGRESS, I COULD BE COMPLETELY WRONG IN ANYTHING I SAY.

To do a proper code review, you need to understand the purpose of the code, what all the stakeholders want. From my own perspective, init scripts work fine, but since Unix companies keep trying to create new init systems, they must have different needs than I do.

Here's a list of the stakeholders. I need to figure out what their goals are.
1) System admins.
2) Desktop users.
3) Distro builders.
5) Android (if systemd turns out to be good enough).
4) Programmers

My suspicion is that systemd has taken over because it makes things easier for 3.

At its core, Unix is a system for programmers. What other system comes with a compiler and multiple interpreters by default? Bash is so much more useable than DOS, or even powershell (yeah, go ahead and flame me but I'm right, Powershell doesn't even have < working). Unix was designed by programmers and for programmers.

The reason I'm talking about it is the traditional init process is incredibly discoverable. All you have to do is look in the /etc/rc directories, and you can figure out how your system boots. You can see it all. For a programmer it's easy. Poking around in the system to understand it is one thing that makes Unix great (and what I like about Slackware: the whole thing is lovingly crafted).

So that describes the approach I am taking to code review, and to the init process. Hopefully Systemd is an improvement.

User Journal

Journal: World Peace is Easy

Journal by phantomfive

World peace is an unusually simple problem: it's entirely a marketing problem. We don't even have to get people to buy anything, all we have to do is get them to want it. The marketing is the whole problem. Once everyone wants it, then the problem is solved because no one will fight anymore. It really is that easy.

In talking to people, I have observed three broad 'market segments' that need to be addressed, three types of people. Maybe there are more, but this is what I have found so far:

1) Those who think that humans are violent by nature, and thus war is inevitable. These are believers in the 'killer ape' theory or perhaps they've just seen too much violence in their lives. Fortunately men are not violent by nature, the 'killer ape' theory is discredited, and in any case we are capable of choosing our destinies.

2) The second group are those who would stop fighting, but the 'other guys' won't stop. These are most Americans. They didn't want to attack Afghanistan originally, but the Afghanis struck first, so what choice was there? These people happily would support peace if they saw it as a viable possibility. Fortunately, peace is viable because it is the most profitable solution, we just need to help the world see that. The more people start supporting peace, the more this group will become convinced that peace is possible.

3) The third group is the most difficult group, because they actually have something to gain from war. In this category was Slobodan Milosevic, who wanted to consolidate power in his country, or warriors on the edge of the Sahara who want to take others' land for their own cattle. Some people fight because it is exciting, they like the thrill. These people need to see that there is a better way, and that their children will want to live in peace, and sometimes compromise is worth it. Anyone who has loved has learned the value of compromise. These people can too.

Try to talk to everyone you can about world peace, because word of mouth is the best type of marketing.

Education

Journal: Religion is falsifiable

Journal by phantomfive

http://slashdot.org/comments.pl?sid=1301347&cid=28687519

Religions are falsifiable (science is the un-falsifiable thing: it is a tool, not a proposition. How do you falsify a hammer? How do you falsify science?). Any decent religious system has ideas of the type, if you do X, then Y will happen. Let's investigate a bit, and see what some religions say:

Buddhism: if you follow the eight-fold path, your suffering will end. Extremely testable. If you follow the eight-fold path, and you are still suffering, then man, they led you astray.

Tantric yoga: do these exercises and meditations and eventually you will have a kundalini rising (enlightenment). So if you do them, and you don't have a kundalini rising, then you know tantra is worthless (either that or your teacher sucks).

The Bible: Those who believe shall be able to do miracles, such as drink poison and not get hurt, or heal the sick (Mark 16:17). So if you follow Christ and you can't do those things, then......yeah, you've just falsified it.

Daoism: 99% of the battle of daoism is figuring out what you are supposed to do. That is an ancient Chinese way of teaching.....but, if you ever do figure out what it is you're supposed to do, then you will be able to tap into the mysterious power of the Dao. If you figure out what you are supposed to do, and do it, and still can't tap into that power, then you've just falsified Daoism.

Mormonism: fast and pray oft, grow in humility, and you will be filled with joy and consolation. I really like Mormonism because it is even more scientific: it says all over the place things like, "if you have faith, God will give you anything that is good." It gives examples of people who became good enough that God gave them anything they asked for, and it says that you can do it too. It even directly gives an example of how to test these claims, and verify/falsify them. I like it because the more clear the promises, the more easily it is falsifiable.

See? If all you are saying is that some being out there exists who affects life on earth in some undetectable way, then yeah, it's pretty pointless. But any preacher who preaches that doesn't know his religion.

Also see:

http://interviews.slashdot.org/comments.pl?sid=39406&cid=4207448

http://interviews.slashdot.org/comments.pl?sid=39406&cid=4208176

User Journal

Journal: Programming Style

Journal by phantomfive

"I'd crawl over an acre of 'Visual This++' and 'Integrated Development That' to get to gcc, Emacs, and gdb. Thank you." (By Vance Petree, Virginia Power)

Amen.

If you think nobody cares if you're alive, try missing a couple of car payments. -- Earl Wilson

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