Question
The lock file /var/lib/dpkg/lock-frontend still exists between apt-update and apt-install
- Posted on August 13, 2021
- DigitalOcean DropletsUbuntu 20.04
Asked by academyJellyfish
Hi,
I am creating a droplet (nyc1/4vcpu-8gb/ubuntu-20-04-x64) with doctl and, when accessible (ping on ip address followed by nc on ssh port) I send and run the following bash script:
#!/bin/bash
apt-get update
apt-get install -y apt-transport-https \
curl \
tmux \
zsh \
zip \
inotify-tools
But for some reason there is some kind of race condition between the apt-update and apt-install because the lock file (/var/lib/dpkg/lock-frontend) seems not to be released, like the following snippet:
Get:29 http://archive.ubuntu.com/ubuntu focal-backports/main amd64 Packages [2,568 B]
Get:30 http://archive.ubuntu.com/ubuntu focal-backports/main Translation-en [1,120 B]
Get:31 http://archive.ubuntu.com/ubuntu focal-backports/main amd64 c-n-f Metadata [400 B]
Get:32 http://archive.ubuntu.com/ubuntu focal-backports/universe amd64 Packages [5,800 B]
Get:33 http://archive.ubuntu.com/ubuntu focal-backports/universe Translation-en [2,068 B]
Get:34 http://archive.ubuntu.com/ubuntu focal-backports/universe amd64 c-n-f Metadata [288 B]
Fetched 5,354 kB in 2s (2,995 kB/s)
Reading package lists... Done
E: Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 2194 (apt-get)
N: Be aware that removing the lock file is not a solution and may break your system.
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?
Am I doing something wrong or maybe is it a bug?
Cheers,
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You’re not wrong but you are possibly confused. I was too confused encountering similar problems.
TLDR: The lock is being released between
apt-get updateandapt-get installcommands. That the opposite may appear true is a red herring.Another process (likely the digitalocean local agent) is installing packages by running
apt-get install.Use
apt installinstead ofapt-get install. The former waits for the lock to be released.Detailed answer: According to an answer on a related question “DigitalOcean’s local agent is also doing an apt-get update right after the droplet comes alive”.
If the digitalocean local agent is running
apt-get <cmd>at the same time that you are runningapt-get <cmd>(as I think was the case for me), you may think that the error relates to yourapt-getprocess whereas it may not. This was the source of my confusion.Solution (of sorts …): Use
apt installinstead ofapt-get install. The former waits for the lock on/var/lib/dpkg/lock-frontendto be released.Troubleshooting help: Here is an example of how I helped myself figure out what was going on and helped me realised that it was not my
apt-getprocess that was being referred to in the error message.Running
echo $$shows our script’s PID. Thepsoutput for the process runningapt-get installwill show a different PID.And on close inspection, the currently-running
apt-get installcommand that you will see listed will very likely not match your ownapt-get installcommand (unless by extreme coincidence).I tried switching from
apt-get installtoapt installpurely to be sure that ifapt-get installis seen to be running then I know it is not of my doing. By sheer luck this also highlighted a lovely workaround which I’m happy with.