Category Archives: UNIX & Linux

Debian /boot old kernel images

So I was looking at yet another failed apt-get upgrade because /boot was full. After my initial whining on Twitter, I immediately received a hint towards /etc/apt/apt.conf.d/01autoremove-kernels, which gets generated from /etc/kernel/postinst.d/apt-auto-removal after the installation of new kernel images. The … Continue reading

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How expiration dates in the shadow file really work

tl;dr: Accounts expire as soon as UTC reaches the expiration date. In today‘s installment of my classic shame-inducing series “UNIX basics for UNIX professionals”, I want to talk about account (and password) expiration in /etc/shadow on Linux. The expiration time … Continue reading

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SSH firewall bypass roundup

So my SSH workflow has reached a turning point, where I’m going to clean up my ~/.ssh/config. Some entries had been used to leverage corporate firewall and proxy setups for accessing external SSH servers from internal networks. These are being … Continue reading

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CentOS 7 on MD-RAID 1

Figuring this out took me quite a bit of time. In the end, I approached the starter of this hilariously useless CentOS mailing list thread, who assured me that indeed he had found a way to configure MD-RAID in the … Continue reading

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What does the slash in crontab(5) actually do?

That’s a bit of a stupid question. Of course you know what the slash in crontab(5) does, everyone knows what it does. I sure know what it does, because I’ve been a UNIX and Linux guy for almost 20 years. … Continue reading

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OpenSSH connection multiplexing

The Challenge I was in touch with a developer the other day who used SSH to programmatically connect to a remote machine where he would start some kind of processing job. Unfortunately, he was in trouble when he wanted to … Continue reading

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Using the SSH agent from daemon processes

One of my more recent installations, the BackupPC server I wrote about earlier, needs full access as the user root to his clients in order to retrieve the backups. Here’s how I implemented authentication on this machine. BackupPC runs as … Continue reading

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Swap im Reality Check

Swap unter Linux scheint so eine Sache zu sein, um die sich reichlich Mythen und Legenden ranken. Deshalb schreibe ich heute mal auf, was ich so von der Sache halte. Wie wir alle wissen, wird der Swap-Bereich zusammen mit dem … Continue reading

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