DevOps

General technical system administration and devops documentation.

Linuxඞ

General Linux tidbits.

APT upgrades without automatic restartsඞ

On modern apt based systems if you wish to control the restarts better then you can export these vars before upgrade:

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1 2	`export DEBIAN_FRONTEND=noninteractive export NEEDRESTART_MODE=l # l - list only, a - auto restart, i - interactive restart`

Sudo and rootඞ

You may see sudo su - used instead of sudo -i but there are some subtle differences between them. The sudo su - command sets up the root environment exactly like a normal login because the su - command ignores the settings made by sudo and sets up the environment from scratch. The default configuration of the sudo -i command actually sets up some details of the root user's environment differently than a normal login. For example, it sets the PATH environment variable slightly differently. This affects where the shell will look to find commands. You can make sudo -i behave more like su - by editing /etc/sudoers with visudo. Find the line

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1	`Defaults secure_path = /sbin:/bin:/usr/sbin:/usr/bin`

and replace it with the following two lines:

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1 2	`Defaults secure_path = /usr/local/bin:/usr/bin Defaults>root secure_path = /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin`

For most purposes, this is not a major difference. However, for consistency of PATH settings on systems with the default /etc/sudoers file, it must be considered.

SSHඞ

Fix SSH permissionsඞ

Bash
find .ssh/ -type f -exec chmod 600 {} \;; find .ssh/ -type d -exec chmod 700 {} \;; find .ssh/ -type f -name "*.pub" -exec chmod 644 {} \;

Virtualizationඞ

Check nested virtualization supportඞ

Intel:

cat /sys/module/kvm_intel/parameters/nested
modinfo kvm_intel | grep -i nested

AMD:

cat /sys/module/kvm_amd/parameters/nested
modinfo kvm_amd | grep -i nested

Diskඞ

Check if disk is SSD or HDDඞ

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1	`lsblk -d -o name,rota`

CPU sockets and coresඞ

Only use first CPU socket for a task:

Bash
numactl --cpubind=0 --membind=0 <COMMAND>

Check which cores are E-cores (efficiency cores) and run task only on P-cores (performance cores):

Bash
cat /sys/devices/cpu_atom/cpus
12-19

taskset -c 0-11 <COMMAND>