LCA ICT Specialism flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

What does /etc contain?

Host-specific configuration files: network settings, service configuration, user account files, and startup configuration. It is text-based and edited by administrators, not by package managers at runtime.

Meaning of 2>&1

Redirects file descriptor 2 (stderr) to the same destination as descriptor 1 (stdout), so both streams appear in one place. Order matters: it must follow the stdout redirection.

grep -r versus grep -n

-r searches directories recursively through all files; -n prefixes each matching line with its line number. They combine: grep -rn pattern dir shows file, line number, and match.

find -exec terminator

Ending with \; runs the command once per matched file. Ending with + batches many files into one invocation, which is faster for large result sets.

chmod 750 meaning

Owner gets read, write, execute (7); group gets read and execute (5); others get nothing (0). Applied to a directory, others cannot list or traverse it.

Zombie process definition

A process that has exited but whose parent has not yet called wait() to collect its exit status. It holds a process table entry but no memory; killing it is ineffective and the parent must reap it.

SIGTERM versus SIGKILL

SIGTERM (15) requests graceful termination and can be caught or ignored so the process can clean up. SIGKILL (9) cannot be caught or ignored and terminates immediately, risking data loss.

nice value range

Runs from -20 (highest scheduling priority) to 19 (lowest). Default is 0. Only root can lower the value; unprivileged users can only increase it for their own processes.

systemctl enable versus start

start runs the unit now; enable creates the symlinks so the unit starts at boot. A unit can be enabled but not running, or running but not enabled.

Load average interpretation

Average number of runnable and uninterruptible tasks over 1, 5, and 15 minutes. Compare to CPU count: sustained values above the core count indicate saturation.

Private IPv4 address ranges

10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. They are not routable on the public internet and require NAT or a proxy for external access.

Usable hosts in /24

A /24 leaves 8 host bits, giving 256 addresses. The network and broadcast addresses are reserved, so 254 addresses are assignable to hosts.

169.254.x.x address meaning

An IPv4 link-local address assigned when DHCP fails. It allows local link communication only and signals that the client could not obtain a lease from a DHCP server.

ss -tuln purpose

Lists TCP and UDP listening sockets in numeric form without resolving names. It shows which ports a host accepts connections on, useful for verifying a service is bound.

DNS lookup order

Determined by the hosts line in /etc/nsswitch.conf. With 'files dns', /etc/hosts is checked first, then the nameservers listed in /etc/resolv.conf.

DHCP DORA sequence

Discover (client broadcast), Offer (server proposes lease), Request (client accepts), Acknowledge (server confirms). Uses UDP ports 67 on the server and 68 on the client.

MBR versus GPT

MBR supports four primary partitions and disks up to 2 TiB. GPT supports 128 partitions by default and disks larger than 2 TiB, with redundant headers for recovery.

Sticky bit on directories

Numeric 1000. In a directory such as /tmp, it allows users to delete only files they own, even when the directory is world-writable. Shown as t in ls -l.

umask 022 result

Masks group and other write from defaults. New files become 644 (rw-r--r--) and new directories 755 (rwxr-xr-x). The mask is subtracted from 666 and 777 respectively.

Inode exhaustion symptom

df -h shows free space while writes fail with 'no space left on device'. df -i confirms 100% inode use; many small files consume inodes even when blocks remain.

fstab nofail option

Allows the boot process to continue when the device is missing or fails to mount. Without it, a missing entry can drop the system into emergency mode.

LVM component order

Physical volumes are grouped into a volume group, which is divided into logical volumes that hold filesystems. This allows resizing and spanning multiple disks.

setuid binary risk

A file with the setuid bit runs with the owner's privileges, often root. Misconfigured setuid programs are common privilege-escalation paths, so they are audited regularly.

SELinux enforcing versus permissive

Enforcing blocks policy violations and logs them. Permissive only logs violations without blocking, which is useful for testing policy before enabling enforcement.

visudo purpose

Safely edits /etc/sudoers with syntax checking and file locking. A syntax error in sudoers can lock out all administrative access, so direct editing is avoided.

SSH key authentication hardening

Set PasswordAuthentication no and PermitRootLogin no in sshd_config, distribute public keys in authorized_keys, and restart sshd. Private keys never leave the client.

Script shebang line

The first line, such as #!/bin/bash, names the interpreter with an absolute path. The kernel uses it to run the script when executed directly; without it the shell may interpret the file.

set -euo pipefail effect

Aborts on command failure (-e), on undefined variables (-u), and on failures within pipelines (-o pipefail). It turns silent errors into early script termination.

Cron field order

Minute, hour, day of month, month, day of week, then the command. An asterisk matches all values; @reboot runs once at startup instead of on a schedule.

Container versus virtual machine

Containers share the host kernel and isolate processes with namespaces and cgroups, so they start quickly. VMs run a full guest OS on a hypervisor with stronger isolation.

Shared responsibility model

The cloud provider secures physical infrastructure and the hypervisor. The customer secures operating systems, identities, access control, and data, with more customer responsibility in IaaS.

Backup 3-2-1 rule

Keep three copies of data, on two different media types, with one copy offsite. Restores must be tested; an untested backup does not demonstrate recoverability.