PostgreSQL 8.3 adding uuid-ossp on Debian

UUID is a nice way to generate (almost) unique id’s.

However on PostgreSQL 8.3 the data type exists, but if you wish to be able to generate UUID’s you need to get a module (in this case uuid-ossp).

On Debian this module is in the contrib package, so if you have not installed this before do it now

user@server:~$ sudo apt-get install postgresql-contrib

Then you need to “load” the module into PostgreSQL; or more accurately you tell PostgreSQL about the new functions this module has, how to reach them etc.
Depending on you security settings (in pg_hba.conf) you may need to log in as the postgres user on your system.

postgres@sever:~$ psql -d MYDB -U postgres -f /usr/share/postgresql/8.3/contrib/uuid-ossp.sql

Ubuntu Hibernate/Suspend problem

First off, quick explanation.
Suspend saves a image to ram. It is faster to save and reload; but the computer uses a minimal amount of energy to keep this in ram. If the power is lost (battery is drained etc) then the image is lost.
Hibernate save a image to disk. It is slightly slower to save and reload; but there is no problem if the power is lost.

However I am not the only one that have noticed that hibernate/suspend on Ubuntu does not work on a default installation.
One solution that more than me have found to be working is to switch to uswsusp.

user@laptop$ sudo apt-get install uswsusp
user@laptop$ sudo s2disk

s2disk does a hibernation (s2ram does a suspend); and it is good to test it out before swapping the hibernate/suspend function.
When you know hibernate/suspend works, you can swap to using uswsusp by using:

user@laptop$ sudo dpkg-divert --rename --divert /usr/sbin/pmi-disabled /usr/sbin/pmi

If you later on would like to swap back you can use

user@laptop$ sudo dpkg-divert --rename --remove /usr/sbin/pmi

apt-get WARNING: The following packages cannot be authenticated!

apt-get is verifying the packages before installing them.
If the keys are not up to date, then apt-get upgrade will issue a warning.

WARNING: The following packages cannot be authenticated!
  ure uno-libs3
Install these packages without verification [y/N]?

The way to solve this is rather simple, just run apt-get update and it should download the keys automatically.

apt-key handles keys, using apt-key list will show you the keys that are on the computer.

Limit the download speed of apt-get

Sometimes it is nice to limit the download speed of apt-get.

The way I do this is to create a file “/etc/apt/apt.conf.d/76download” and enter the following to it

Acquire{Queue-mode "access";http{Dl-Limit "50";};};

This will limit apt-get to at most 50 kb/s for apt-get.
Some other how to’s suggest the use of dl-limit but be adviced, dl-limit is per each connection apt-get does (normally it does 2 at a time); the one used above caps apt-get in total.

ubuntu: Upgrade release version

  1. Check out “/etc/update-manager/release-upgrades” to make check out what sort of releases you wish to use (lts/normal/or never upgrade)
    # default behavior for the release upgrader
    # default prompting behavior, valid options:
    #  never  - never prompt for a new distribution version
    #  normal - prompt if a new version of the distribution is available
    #  lts    - prompt only if a LTS version of the distribution is available
  2. Make sure the (current) dist is up to date. Problems are not guaranteed if you don’t – but they are likely
    • apt-get update
    • apt-get upgrade
  3. Make sure the upgrade tool is installed (and up to date) “apt-get install update-manager-core”
  4. do-release-upgrade
  5. Follow the instructions

What program is using port x?

netstat can be used to figure out what program is using a port.

$ netstat -nlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0    *               LISTEN      1096/sshd
tcp        0      0    *               LISTEN      1733/apache2
tcp6       0      0 :::22                   :::*                    LISTEN      1096/sshd
Active UNIX domain sockets (only servers)
Proto RefCnt Flags       Type       State         I-Node   PID/Program name    Path
unix  2      [ ACC ]     STREAM     LISTENING     6338     1071/gdm-simple-sla @/tmp/gdm-greeter-LvjLQPzT
unix  2      [ ACC ]     STREAM     LISTENING     5165     1072/X              /tmp/.X11-unix/X0

If you have a lot open then grep can be used to only find what you are looking for

netstat -nlp|grep :22
tcp        0      0    *               LISTEN      1096/sshd
tcp6       0      0 :::22                   :::*                    LISTEN      1096/sshd

For windows, simply start with

netstat -n

apt-get update gives the error “E: Could not get lock /var/lib/apt/lists/lock – open (11: Resource temporarily unavailable)”

If running apt-get (or aptitude) and you get the following error:

$ apt-get update
E: Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the list directory

Then (most likely) explenation is that one of the sources have gotten a timeout and that a (cron) sheduled update task have gotten locked.
A simple solution for this is to find the cron process is locked, and kill it.

$ ps -a |grep apt
Warning: bad ps syntax, perhaps a bogus '-'? See
 3737 ?        SN     0:00 /bin/sh /etc/cron.daily/apt
 3833 ?        SN     0:00 apt-get -qq -y update -o APT::Update::Auth-Failure::=cp /usr/share/apt/apt-auth-failure.note /var/lib/update-notifier/user.d/
 3835 ?        SN     0:00 /usr/lib/apt/methods/http
 3838 ?        SN     0:00 /usr/lib/apt/methods/http
 3842 ?        SN     0:00 /usr/lib/apt/methods/http
 3869 ?        SN     0:00 /usr/lib/apt/methods/http
 4223 pts/0    R+     0:00 grep apt
$ kill -9 3833

If this happens often, then perhaps you should try to debug the sources and remove (or exchange) the source that is causing the problems.

sudo without password

Use visudo to edit /etc/sudoers

user host = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm

user, host and or the list of commands to be run can be swapped with the keyword ALL.
However that is probably not a good idea in most cases.

more info on this is in the manpages sudoers(5)

Ubuntu: Buffer I/O error on device sr0 logical block

Most of the time this error occurs that is a bad disk or a bad drive (or a bad cable).
Ubuntu 8.10 seams (from own experience and google) to be commonly affected by this.

You can try the following (I try them in this order)

  • If you only get buffer errors and no CRC errors, just try and wait (a few minutes) It might still be possible to install
  • Try another installation CD [from the same installation image] – if this works, then the other disk is bad
  • Try to swap out the cable to the drive (if you have a ribbon cable use one with 80 connectors, not one with 40)
  • Try to swap out the drive
  • Try another installation CD [from another installation image, old version, other dist, windows] – if this works then there is an issue with the installation image – there might be an issue worth reporting

If all this fails or you wish to install the version you have, then using a usb stick to install the image might be a good idea.

apt-get update The following packages have been kept back

 apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages have been kept back:
  bind9-host dnsutils libbind9-50 libdns50 libisc50 libisccc50 libisccfg50 liblwres50 linux-generic linux-generic-pae linux-image-generic
0 upgraded, 0 newly installed, 0 to remove and 12 not upgraded.

The message has been kept back most often means that the upgrade was kept back due to dependencies that are not met.

Some possible solutions

  • A simple way is to invoke dselect to help out with the update. dselect performs the actions necessary to realize that state (for instance, the removal of old and the installation of new packages).
     apt-get dselect-upgrade
  • While apt-get and aptitude are basically the same, aptitude is sometimes better at handling dependencies than apt-get
     aptitude upgrade
  • Another solution is to install the package using apt-get install to install the upgraded package and let apt-get install the missing dependencies
     apt-get install dnsutils