DevOps

General technical system administration and devops documentation.

Linuxඞ

General Linux tidbits.

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

Text Only
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

Text Only
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>