High Tech Sorcery

I’m planning on buying/building a new computer and I think I will install Ubuntu 10.10 on it.  My plan is to use btrfs for the first time.  Risky, but I will be taking nightly backups.  However, Ubuntu 10.10 is planning on shipping with the Linux 2.6.35 which has a severe btrfs performance regression as documented here:

• Btrfs Did Regress Hard In The Linux 2.6.35 Kernel
• maverick btrfs slow install

But besides that I’m also hoping that the I/O performance situation will be improved.  It has been very difficult to track down where the bug is but I have certainly experienced it.  I haven’t tested the patches but if they work I hope they find there way into Ubuntu 10.10

• Fix “system goes unresponsive under memory pressure and lots of
  dirty/writeback pages” bug.
• Large I/O operations result in poor interactive performance and high iowait times
• The Linux Desktop Responsiveness Patches Are Feeling Good
• Heavy Disk I/O harms desktop responsiveness
• Very poor desktop response (high latency) during I/O-load with SATA+NCQ

It is extremely difficult to keep up with all the filesystems being developed for Linux these days.  Clearly, so much activity represents an understanding that the current filesystems do not address the needs of users.  However, as is all too often the case, development is extremely fragmented with very small groups each trying to build the 1 true filesystem and thus each effort taking longer than a collaborative project.

What I want from a filesystem: snapshots, replication (local, aka RAID and network), checksums (at least optionally), compression (at least optionally), and some basic intelligence such as when a checksum fails and replication is used to get the data from another replica.  Yes, fast error recovery and good performance are important too.

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So I am trying the WP-SpamFree Anti-Spam plugin for Wordpress.  It uses javascript to prevent spam.  I’m really hesitant because I prefer websites which do not require javascipt for their basic functionality.  Perhaps I will use another spam blocker.  Or perhaps I will just resign myself to accepting that functional javascript is requirement from browsing the web.

Update: I’m going to try the NoSpamNX plugin instead.  It does not require cookies or javascript.  We’ll see how it goes.

I think Ubuntu 9.04 is the only version of Ubuntu suffering from this bug but it appears as though no fix for this serious regression will be forthcoming.  To get pygrub to work you actually have to fix a bug in the python 2.5 curses library.  Open “/usr/lib/python2.5/curses/__init__.py” and add the following lines starting at line 17:

import os as _os
import sys as _sys

After that pygrub should work correctly.  More information about this bug can be found in launchpad bug #395321.

Just got done helping a user debug connection problems using FileZilla to connect over SFTP/SSH.  I noticed, sadly not immediately, that the username he was using was being send with an extra space at the end and thus was an invalid user.  I’m not sure there is a valid reason not to trim/strip whitespace from the beginning and ending of a username.  But this is something to be aware of.

I sent this to a client who didn’t know how to enable remote desktop administration in windows.

In the olden days one had to use packages such as scponly and rssh in order to restrict a user account to just being able to use scp and sftp.  Now that functionality is built into OpenSSH.  A client wanted me to setup such an account for 1 user on a system.  I modified sshd_config like this:

Match user username
  ChrootDirectory /home/%u
  ForceCommand internal-sftp
  X11Forwarding no
  AllowTcpForwarding no

Note that this only works in Ubuntu 8.10 and later and Debian 5.0 and later.  Also, be aware that the home directry has to be owned by root and not writable by the user for security reason.  So a directory inside the home directory will need to be created for the user to upload any files.

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