Which uninstalled package provides a file?

$ apt-file find guestmount
guestmount: /usr/bin/guestmount
guestmount: /usr/share/bash-completion/completions/guestmount
guestmount: /usr/share/doc/guestmount/changelog.Debian.gz
guestmount: /usr/share/doc/guestmount/copyright
guestmount: /usr/share/man/ja/man1/guestmount.1.gz
guestmount: /usr/share/man/man1/guestmount.1.gz
guestmount: /usr/share/man/uk/man1/guestmount.1.gz

Scripting DNS lookups

Are you writing a script and some command doesn’t accept hostnames and you don’t want to inline the IP address? dig +short is your friend!

$ dig +short gbenson.net
69.163.152.201

Which APT repository did a package come from?

$ apt policy wget
wget:
  Installed: 1.21.2-2ubuntu1
  Candidate: 1.21.2-2ubuntu1
  Version table:
 *** 1.21.2-2ubuntu1 500
        500 http://gb.archive.ubuntu.com/ubuntu jammy/main amd64 Packages
        100 /var/lib/dpkg/status

Python debugger

By the way, if you’ve never used Python’s debugger, it really is as simple as adding a call to the built-in function breakpoint() at the point you want it to stop.

sed trick

I discovered a new sed trick today:

sed -i~

“I” stands for “in place”. It edits the files in place! And makes a backup if you want!

Container debugging minihint

What’s in my container?

$ podman ps --ns
CONTAINER ID  NAMES            PID    CGROUPNS  IPC         MNT         NET         PIDNS       USERNS      UTS
fe11359293e8  eloquent_austin  11090            4026532623  4026532621  4026532421  4026532624  4026531837  4026532622

$ sudo ls -l /proc/11090/root/
total 22628
lrwxrwxrwx.   1 root root        7 Jul 25  2019 bin -> usr/bin
dr-xr-xr-x.   2 root root        6 Jul 25  2019 boot
drwxr-xr-x.   5 root root      360 Jan 24 12:03 dev
drwxr-xr-x.   1 root root      183 Jan 23 16:43 etc
 ...

Thank you.
[28 Jan@1135UTC] UPDATE—Actually, this doesn’t seem to work with newer systems, sorry!

GNOME 3 won’t unlock

Every couple days something on my RHEL 7 box goes into a swapstorm and uses up all the memory. I think it’s Firefox, but I never figured out why, generally I have four different Firefoxes running with four different profiles, so it’s hard to tell which one’s failing (if it even is that). Anyway, sometimes it makes the screen lock crash or something, and I can’t get in, and I can never remember what process you have to kill to get back in, so here it is: gnome-shell. You have to killall -9 gnome-shell, and it lets you back in. Also killall -STOP firefox and killall -STOP "Web Content" are handy if the swapstorm is still under way.

Building GDB on a freshly installed machine FAQ

So you just installed Fedora, RHEL or CentOS and now you want to build GDB from source.

How do you make sure everything you need to build it is installed?
```
# dnf builddep gdb
```
Did it say, No such command: builddep? Do this, then try again:
```
# dnf install dnf-plugins-core
```
Did it say, dnf: command not found…? You’re using yum, try this:
```
# yum-builddep gdb
```
Did it say, yum-builddep: command not found…? Do this, then try again:
```
# yum install yum-utils
```

Thank you, you’re welcome.

Python hacking

Python‘s had this handy logging module since July 2003. A lot of things use it, so if you’re trying to understand or debug some Python code then a handy snippet to insert somewhere is:

import logging
logging.basicConfig(level=1)

Those two lines cause all loggers to log everything to the console. Check out the logging.basicConfig docs to see what else you could do.