How to show apt log history

Users of Debian-based distributions (myself included) often brag about Debian's supposedly superior package management tool-set. This tool-set includes a choice of several excellent package managers such as dpkg, apt, synaptic, and aptitude. The various tools are all first class at what they are designed to do.

In my opinion, one major feature gap is a command-line interface for viewing the apt change log. After a recent routine Etch package upgrade, I discovered that the grub menu.lst file got corrupted. So, I wanted to check the recent apt activities to find out which packages were the possible suspects.

A google search revealed that viewing change history is not that simple. Aptitude writes change log info to /var/log/aptitude. Synaptic users can get the same info through its graphical user interface. But is there a standard change log file that the most common Debian package managers write to? The second question is whether there exists a command-line tool for accessing it.

It turns out that such a log exists, and it is /var/log/dpkg.log. This is a single log file that records all the apt activities, such as installs or upgrades, for the various package managers (dpkg, apt-get, synaptic, aptitude).

Regarding a command-line tool for accessing apt history, there used to be a package named apt-history for viewing apt-get activities. Its web site suggests that work in the project has been discontinued due to the fact that dpkg now does logging. It went on to recommend the use of a simple bash function (also named apt-history) to access the log file (/var/log/dpkg.log)

Below is the bash function from that web site.

function apt-history(){
      case "$1" in
        install)
              cat /var/log/dpkg.log | grep 'install '
              ;;
        upgrade|remove)
              cat /var/log/dpkg.log | grep $1
              ;;
        rollback)
              cat /var/log/dpkg.log | grep upgrade | \
                  grep "$2" -A10000000 | \
                  grep "$3" -B10000000 | \
                  awk '{print $4"="$5}'
              ;;
        *)
              cat /var/log/dpkg.log
              ;;
      esac
}

I've tried it, and it works.

To set it up, insert the above code into /root/.bashrc.

To run apt-history, you need to become root (for example, sudo -i). Entering apt-history with no parameter will simply dump the change log file. To select what activities you want to see, you can enter one of install, upgrade, remove, rollback as a single parameter to apt-history.

$ sudo -i
Password:
# apt-history install
2008-08-01 21:37:00 install googlizer  0.3-3
2008-08-09 08:20:54 install agrep  4.17-3
2008-08-09 08:28:26 install abuse-frabs  2.10-7
2008-08-09 08:28:27 install abuse  1:0.7.0-5
#

Learn more about a command when no man info page is available

To read the documentation about a command, the first thing we do is to read its manual (man) page.

$ man cd
No manual entry for cd

But what if no man page is available for that command?

This could be due to a number of different reasons. For example, the Linux system was originally installed without any man pages at all. I worked with a Linux-based mobile gateway device that has 0 man pages pre-installed. This is to save disk space on a 1 GB Solid State Drive (SSD). In most typical desktops or servers, man pages are pre-installed.

A man page can be missing for a particular command because the administrator, for whatever reason, did not install the man page for that command. If that is the case, google is your best friend. The challenge here is to narrow down the search to get to the man page quickly.

There is yet another reason why there is no man page for a command. If it is a bash shell built-in command, it will NOT have its own man page. Documentation is still available but it is a bit harder to get to it. It turns out that information about bash built-in commands can be found inside the bash man page. You simply enter man bash, and search for the SHELL BUILTIN COMMANDS section (using the command /^SHELL BUILTIN). Then scroll down until you reach the built-in command you are looking for.

$ man bash

How do you know if something is a bash built-in command in the first place?

Use the type command (another bash built-in).

$ type cd
cd is a shell builtin 

Note that not all Linux distributions behave the same way when you man a bash built-in command. Debian Etch, the distro I use at home, reports no man page when you man cd. Some distributions, like the Red Hat-based Centos, will display the bash man page. In this case, you are one step ahead of the rest.

Pondus: A personal weight management software

A week after my return from a New England & Canada cruise, I found myself busy searching for a personal weight management software.

Why weight management? See the chocolate dessert buffet pictures taken on board the Holland America Maasdam cruise ship.

I came across pondus, a python program that is free and open-sourced.

Pondus has a rather modest feature set: the ability to enter one's weight over time, and have it plotted in a chart. It does not have too many bells and whistles, but it is very simple to use.

Pondus is packaged with certain Debian releases (namely, Lenny and Sid). So a simple apt-get install pondus will put it on your system. Because I run Debian Etch, I need to install it from source files.

I downloaded the source tar ball as well as the install instructions from here. The instructions are straight-forward, and I installed pondus without a glitch.

To run pondus, just type pondus in the command line. When you run pondus for the first time, it is not too terribly exciting .... because you have not entered any weight data.

Before you enter your weight, you should customize the unit of measure that pondus will use(lbs versus kgs). Click on the Tool icon (the one with the screwdriver and wrench) to bring up Preferences. For me, I prefer pounds (that is the unit my scale uses).

Now, let's enter some weight data, and draw a pretty chart.

To enter a weight, click on the Plus icon.

To plot the data, click on the Chart icon.

Pondus has some additional useful features such as data import and export in CSV format, as well as the ability to save the chart in png or svg (2-dimensional vector graphics) format.

An interesting feature is that you can set time-sensitive goals (aka, Weight Planner). For example, you can set a goal such as "weigh 180 lbs on August 15". This feature is disabled by default. To enable it, bring up Preferences as above, and click Use Weight Planner checkbox to select it, and choose whether to include the weight plan in your plots. Note that this feature is not for everyone (do I really need yet another remainder of my shortcomings?)

Pondus is adequate for tracking my body weight. I'm still searching for software that can also track my blood pressure. Won't it be perfect if a single software can manage both weight and blood pressure?

How to do reverse DNS lookup

Most people can better remember domain names, e.g., www.gnu.org, than their corresponding IP addresses, 199.232.41.10. (In this example, www.gnu.org is the home of the Free Software Foundation.) We delegate the responsibility to machines, aka, the DNS servers, to resolve the domain names for us.

Sometimes, we do need to manually lookup the IP address of a domain name. You may already be familiar with the nslookup command which is now deprecated. We use the dig command to make DNS queries.

 $ dig +noall +answer www.gnu.org
www.gnu.org.            67      IN      CNAME   gnu.org.
gnu.org.                67      IN      A       199.232.41.10

The IP address is displayed in the A record, and is 199.232.41.10.

The +noall, +answer combination basically tells dig to only report the answer of the DNS query and skip the rest of the output.

You can also use the dig command with the -x option to do a reverse DNS lookup. A reverse DNS lookup means you want to look up the domain and host name of an IP address.

 $ dig +noall +answer -x 199.232.41.10
10.41.232.199.in-addr.arpa. 36000 IN    CNAME   rev-c41-10.gnu.org.
rev-c41-10.gnu.org.       300     IN      PTR     www.gnu.org.

The PTR record is the one that contains the domain host name. The domain name is, as you expect, www.gnu.org.

Note that PTR records are not required for IP addresses. If a PTR record is not defined for an IP address, you cannot do a remote DNS lookup.

How to count number of files in a directory

Now that I am back from vacation, I had to take care of some chores, like uploading the pictures taken with my digital camera.

I stepped out during the long upload process (400+ pictures). When I returned, it was already done. To just make sure all pictures are now on the server, I wanted to count the number of files in the targetdir directory.

$ ls -1 targetdir | wc -l
454

The above command reads ls dash one piped to wc dash letter l.

Note that if you had used ls dash letter l instead, the count is one greater than the actual number of files. This is because ls dash letter l outputs an extra total line:

$ ls -1 targetdir 
total 529436
-rw-r--r-- 1 peter peter  1510976 Jul 13  2008 DSCN1001.jpg
....

The above method will count symbolic links as well as subdirectories in targetdir (but not recursively into subdirectories).

If you want to exclude subdirectories, you need a heavier duty tool than ls.

$ find targetdir -maxdepth 1 -type f | wc -l

-type f ensures that the find command only returns regular files for counting (no subdirectories).

By default, the find command traverses into subdirectories for searching. -maxdepth 1 prevents find from traversing into subdirectories. If you do want to count files in the subdirectories, just remove -maxdepth 1 from the command line.

Note that the find command does NOT classify a symbolic link as a regular file. Therefore, the above find -type f command does not return symbolic links. As a result, the final count excludes all symbolic links.

To include symbolic links, add the -follow option to find.

$ find targetdir -follow  -maxdepth 1 -type f | wc -l