sip / six digit port number / invalid
While looking through opensips logs of a customer, sometimes we would see the following: ERROR:core:parse_via: invalid port number <110900> ERROR:core:parse_via: <SIP/2.0/UDP 184.108.40.206:110900;branch=z9hG4bKabcdef... ERROR:core:parse_via: parsed so far:<SIP/2.0/UDP 220.127.116.11:110900;branch=z9hG4bKabcdef... ERROR:core:get_hdr_field: bad via As you can see, that 6-digit port number is invalid. Furthermore, when sniffing this traffic, we could see that the port number is almost right. The traffic came from port 11090 (one less zero at the end). Not only the Via header, the Contact header too had the extra appended zero.
openswan klips install / modules
If you want to be able to sniff your IPsec traffic with OpenSwan, you’ll need to get KLIPS instead of the default NETKEY IPsec protocol stack. Installing that on Ubuntu/Karmic should be a matter of: ~# apt-get install openswan-modules-source ~# cd /usr/src /usr/src# tar jxvf openswan-modules.tar.bz2 /usr/src# cd modules/openswan /usr/src/modules/openswan# make KERNELSRC=/lib/modules/`uname -r`/build module module_install But it’s not. Right now, we’re running the default Linux kernel 2.6.31-23-server on this Karmic machine.
mocp / random / enqueue
After disk failure on our company music server, I lost my enqueue-some-random-music-script. That shan’t happen again. So here, for my own enjoyment: autoenq.sh #!/bin/sh enqueue_app="mocp -a" music_glob="*.mp3" music_path="`dirname "$0"`" list_path="$music_path/.autoenq.list" if [ "$*" = "-c" ]; then # Create list of all files find . -type f -iname "$music_glob" > "$list_path.tmp" 2>/dev/null # no lost+found # Create list of all dirs that have files cat "$list_path.tmp" | sed -e 's/\/[^\/]*$//' | sort | uniq > "$list_path" exit 0 fi args="`echo "$*" | sed -e "s/['\\\\]//g"`" # no backslashes and single quotes please args="`echo "$args" | sed -e 's/[[:blank:]]\+/.
asterisk dialplan peculiarities / regex with eqtilde
In the Asterisk PBX dialplan, expressions can be formed using the $[...] syntax. Addition, subtraction, comparison and so on are defined. As is a regex operator: =~ Unfortunately, the documentation about the details of the implementation is hard to find. Here, a breakdown of my findings: static struct val * op_eqtilde is defined in main/ast_expr2.y It uses the REG_EXTENDED flag when calling regcomp: so extended regular expression syntax is used.
executing remote command / ssh / extra escaping
If you use ssh to run commands remotely, you may have run into the problem that you need an extra layer of escaping. Let’s say you have application myapp that for some reason only runs on host myserver. If you have functional ssh keys to log onto myserver it can be helpful to create a myapp wrapper on your desktop. After all, this: $ myapp myargs … is far more convenient than doing this:
django / query expression / negate
Suppose you have an is_enabled boolean in your Django model. class Rule(models.Model): is_enabled = models.BooleanField(blank=True) # other exciting fields here And now imagine you want to negate the is_enabled values. Something you would easily do in SQL, with: UPDATE myapp_rule SET is_enabled = NOT is_enabled; The Django F-syntax is nice, and looks like it should be up for the task. Let’s sum up a couple of attempts: Rule.objects.update(is_enabled=(not F('is_enabled'))) No! You get this:
mysql issue warnings / cron
I’ve previously written about MySQL pain in the behind issues involving views with SECURITY DEFINER and bad client collation selection. For the former problem, I wrote a script that you could call periodically to warn you of potential problems with your views. Now I’ve extended it to warn you about collation issues as well. Put warn-mysql-issues.sh (view) in your cron tab and run it periodically. It’ll save you from production-time errors that you get when attempting to compare a string of one collation with another.
linux / canon mf8350 / printer driver
Getting printer drivers for the Canon MF8350 to work under Ubuntu is a big pain in the behind. (Installation using custom scripts that abuse both /usr/lib and /usr/local/lib and ultimately fail to compile for obscure reasons.) My colleague found that the easiest way to get it to work, was converting the RPM to DEB using alien(1). For your enjoyment, here are the two debian packages needed for Ubuntu 10.04 (amd64):
diff / memory exhausted / udiff
Sometimes when I’m unsure what a button in a database-driven application does, I simply click it and check the differences in the database before and after the click. If the database dumped is (somewhat) sorted and with one line per row (for MySQL use –skip-extended-insert), this can be an easy method of verifying that your application action does exactly what you expect and nothing more. Create a pre.sql before the click, click the button and watch the action happen.
pcap / capture fragments / udp
When dealing with internet protocols that operate on top of UDP, fragmenting suddenly becomes a lot less uncommon. Normally, you would only encounter fragments on TCP connections when the MTU on the sending host is larger then the MTU in any of the next hops. Hosts usually attempt to avoid fragmentation for obvious reasons. (Inefficiëncy, extra reassembly work.) For connectionless UDP packets this is a different matter. Protocols over UDP expect packets to be single entities.