dig: segmentation fault on UML

20 June, 2005 @ 11:33 · Filed under Linux

The ‘Native Posix Thread Library’ (NPTL) is not supported by User Mode Linux (UML). NPTL is the much-vaunted ‘new’ threading implementation in the Linux 2.6.x kernels. There can be many symptoms of this problem, but the one I seem to always get is a crash whenever a program tries to resolve a host name. Whatever the symptoms, you will only see problems with a 2.6.x UML kernel – the same filesystem will work correctly when you boot it with a 2.4.x UML kernel.

The solution: Disable the new threading by renaming /lib/tls to /lib/tls.DISABLED on the guest, and reboot UML.

Although this solution is simple, it’s not permanent (at least on Debian). apt will continue to re-create the /lib/tls directory whenever it is updated. Then you’ll start to see crashes again when you next reboot.

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  1. Arhuaco said,

    30 September, 2005 @ 01:46

    Was here myself. Looking for javascript mutexes.

  2. Placid said,

    18 July, 2007 @ 21:26

    Thanks for this, was quite a handy insight. I’ve been getting very slow responses from w (or who) as well as top, and just recently received a segmentation fault (segfault) from a w. Wish there was a better solution, as rebooting UML (my webserver is a VPS running on UML) isn’t an option, but I need a 2.6.x kernel for some kernel-space functions related to MySQL :|

    Oh well, maybe UML will get NPTL support :P

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