Sysadmin Cards

It allows users to define shortcuts and configuration options (like Hostname, User, Port, IdentityFile) for SSH connections.

600 (read/write for owner only).

A Canonical Name record that maps one domain name (alias) to another domain name (canonical).

A Mail Exchange record that specifies the mail server responsible for accepting email messages on behalf of a domain.

rsyslog is a traditional syslog daemon that writes logs to text files (e.g., /var/log/syslog). journald is part of systemd and stores logs in a binary format, accessible via journalctl.

The tendency of the kernel to move processes from physical memory to swap space (0-100, higher means more aggressive swapping).

killall kills processes by exact name match. pkill kills processes based on name or other attributes (like regex matching or user ID).

It runs a command immune to hangups (SIGHUP), allowing it to continue running after the user logs out.

They are terminal multiplexers that allow managing multiple terminal sessions inside one window and keeping sessions alive after disconnection.

/etc/profile is the global configuration script for all users upon login. ~/.bash_profile is the user-specific configuration script executed for login shells.

su switches user but keeps the current environment variables. su - switches user and loads that user's full login environment (like a fresh login).

blkid