Category: Snippets

Use stdbuf to tee without buffering

Do you want to tee the output of a command to a file, but see it in your terminal too, without buffering? The stdbuf command can do this for you:

$ sudo stdbuf --output=L tcpdump -i any -tttt -n 'udp port 5353' | tee -a tcpdump-mdns
tcpdump: data link type LINUX_SLL2
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on any, link-type LINUX_SLL2 (Linux cooked v2), snapshot length 262144 bytes
2023-06-15 11:55:16.637670 eth0 M   IP 10.0.0.23.5353 > 224.0.0.251.5353: 0 A (QM)? winnebago.local. (28)
2023-06-15 11:55:16.744660 eth0 M   IP 10.0.0.42.5353 > 224.0.0.251.5353: 0*- [0q] 1/0/0 (Cache flush) A 10.0.0.42 (38)
...

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

Container debugging minihint

What’s in my container?

  1. $ podman ps --ns
CONTAINER ID  NAMES            PID    CGROUPNS  IPC         MNT         NET         PIDNS       USERNS      UTS
fe11359293e8  eloquent_austin  11090            4026532623  4026532621  4026532421  4026532624  4026531837  4026532622
  2. $ 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.

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

Thank you, you’re welcome.