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October 21 2010

sourcefrog : Is swap space obsolete?

There was a thread on the CLUG list recently about whether it was still useful to have swap space, now that it's quite affordable to have a gigabyte or more of memory on a desktop machine. I think it is.

Some people have the idea that touching swap space at all is a sign that the machine is very overloaded, and so you ought to avoid it at all costs, by adding enough memory that the machine "never needs to swap". This may have been true on Unix ten years ago, and may still be true on some systems for all I know but it's not true for Linux.

November 17 2009

'/proc/sys/net/ip*/conf/all/* does not actually affect interfaces' - MARC

I was unpleasantly surprised last night that a rogue machine managed to alter the IPv6 default route of one of my servers, despite my sysctl configuration, which disables RA for "all" interfaces during the boot sequence. It also changes the "default" values:
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October 12 2009

Wieviel Speicher brauchst Du denn? - Die wunderbare Welt von Isotopp

Man kann die VSZ also als die 'gemappte' Größe des Prozesses bezeichnen und die RSS als die 'belegte' Größe des Prozesses. Wenn man ein MySQL neu startet sieht man, daß die VSZ schon fast die endgültige Größe des Prozesses erreicht hat (MySQL hat schon einmal alle großen Puffer beim Betriebssystem bestellt und treibt so die Prozeßgröße nach oben). Die RSS ist jedoch noch sehr klein, weil diese bestellten Puffer noch nicht beschrieben wurden und das Betriebssystem daher die entsprechenden Speicherseiten auch noch nicht physikalisch realisiert hat - die Puffer der Datenbank sind noch kalt und die Daten werden nach Bedarf bei den ersten Zugriffen erst einmal von Disk geladen. Über die Zeit wird die VSZ ein wenig steigen (Verbindungen werden aufgebaut und MySQL bestellt noch ein wenig zusätzlichen Speicher) und die RSS nähert sich der VSZ immer mehr an. Die Datenbank im Beispiel da oben hat eine VSZ von etwas über 25G und eine RSS von immerhin 24.2G. Sie läuft schon sehr lange.

May 20 2009


Kon-Boot is an prototype piece of software which allows to change contents of a linux kernel (and now Windows kernel also!!!) on the fly (while booting). In the current compilation state it allows to log into a linux system as 'root' user without typing the correct password or to elevate privileges from current user to root. For Windows systems it allows to enter any password protected profile without any knowledge of the password. It was acctually started as silly project of mine, which was born from my never-ending memory problems :) Secondly it was mainly created for Ubuntu, later i have made few add-ons to cover some other linux distributions. Finally, please consider this is my first linux project so far :) Entire Kon-Boot was written in pure x86 assembly, using old grandpa-geezer TASM 4.0.

May 05 2009

Das bessere Debian? GNU/kFreeBSD - grUNIX

Im Debian Wiki gibt es nun eine kleine Sammlung an Pros für GNU/kFreeBSD. Ein kurzer Auszug: •Cleaner or more standard kernel interfaces •Single /dev implementation via devfs, instead of the 3 discordant ways of handling /dev that Linux provides. •OpenBSD Packet Filter (pf). •Other nice security features, like jails. •Support for NDIS drivers in the mainline kernel. On Linux, NdisWrapper is unlikely to make it into the mainline kernel. •Possible support for ZFS in the mainline kernel. Due to license and patent issues, ZFS is unlikely to appear on Linux. •Some people say that kFreeBSD has better performance and/or stability (especially in disk/filesystem areas). •The FreeBSD kernel might support some hardware which Linux does not support and/or the FreeBSD kernel support might be better (fewer bugs).
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