System Management
Boot and init
Know the chain: firmware (UEFI/BIOS) → GRUB2 → initramfs → systemd as PID 1. GRUB reads a generated grub.cfg; on RPM-family systems edit /etc/default/grub and regenerate rather than hand-editing the file. The initramfs carries the drivers needed to mount root - if a storage driver is missing, boot drops to an emergency shell.
Storage
Partition with parted or fdisk, format with mkfs.*, identify with blkid, and mount persistently via /etc/fstab. Prefer UUID= or LABEL= over /dev/sdX, which can reorder between boots. fstab fields are: device, mountpoint, fstype, options, dump, fsck-order. The sixth field matters - 0 for swap and pseudo-filesystems, 1 for root, 2 for others. LVM layers PV → VG → LV and allows online growth (lvextend -r). Swap is not a mountpoint.
Packages and processes
RPM family uses dnf/rpm; Debian family uses apt/dpkg. Know which tool queries versus installs. Processes: ps, top, nice/renice for priority, signals (TERM is polite, KILL cannot be caught), and systemd-cgls for hierarchy.
Time and logs
timedatectl and chrony handle clock and NTP; journalctl reads the binary journal, rsyslog writes text logs.
Traps: a bad fstab line can make the machine unbootable - add nofail to non-essential mounts and always test with mount -a before rebooting. Runlevels map to targets (3 = multi-user, 5 = graphical). modprobe reads /etc/modprobe.d; lsmod only lists.
Worked rule: new disk, in order - lsblk, parted mklabel gpt + mkpart, mkfs.xfs, blkid, add a UUID line to fstab with nofail, mount -a, then df -h to confirm.