Linux Administration (Advanced) - Deep Dive

Learn how Linux administrators manage users and groups, including root, system, and normal accounts, and use key files like /etc/passwd, /etc/shadow, /etc/group, and /etc/gshadow to control access.

Learn how a normal user uses sudo to read the /etc/passwd and /etc/shadow files, explore the sudoers file, and understand how groups and root privileges govern access.

Explore the /etc/passwd and /etc/shadow files, inspecting their seven-column structure—username, uid, gid, home directory, and login shell—and learn to extract usernames with cut and grep pipelines.

Examine how the /etc/shadow file stores encrypted passwords and account data, including exclamation marks indicating locked accounts, password-age fields, and epoch-based days, and compare its security to the password file.

Add users and groups on a Linux system using add user and groupadd, creating home directories and passwords. Verify changes in /etc/passwd and /etc/group with sudo and man pages.

Add users and groups, set home and shell during creation, change user passwords as root, and assign users to a group; rename the managers group to leaders and verify membership.

Explore advanced user management in Linux: change passwords with passwd, set password aging with chage, configure password expiration warnings, and safely delete or disable accounts with userdel.

Explore file permissions and ownership in Linux, learning owner, group, and other access modes, how to read permissions with ls -l, and the meaning of read, write, and execute.

Learn how to read and modify Linux file permissions with chmod, applying owner, group, and other rights to read, write, and execute.

Learn to compute Linux file permissions using octal values. Map read, write, and execute to 4, 2, and 1, and apply them to user, group, and owner with chmod.

Change file ownership with chown using sudo, specifying a user and group to transfer ownership, and verify with ls -l to confirm the new owner and group.

Explore special Linux permissions, including set user ID permissions (SUID), set group ID permissions (SGID), and the sticky bit; learn their practical uses and safe application.

Master assigning and removing suid permissions for files using octal and symbolic chmod methods. Learn how setuid appears as s or S and apply and remove these permissions.

learn how to assign sgid permissions to a group file using octal and symbolic methods with chmod, enabling group members to execute the file with the group's privileges.

Explore how Linux manages processes, including interactive, batch, zombie, and orphan types, and how the kernel scheduler uses run queues to allocate resources for foreground and background tasks.

Learn to list and inspect running processes with the ps command, understanding pid, tty, time, and cmd columns from /proc. Use -e, -f, and -eaf with grep to filter results.

Explore how to monitor and manage processes with the top and htop tools, view live CPU and memory usage, load averages, and interactively sort, filter, and signal processes.

Learn how to terminate unresponsive or resource-heavy processes using the kill command and signals, differentiate shell builtins from /bin/kill, and apply common signals with examples.

Explore sending signals to processes, using the hang up signal (hup), kill, pkill, and killall, and how processes may catch or ignore signals, soft versus hard kills.

Learn to manage foreground and background processes in Linux administration, including ampersands to run non-interactive background tasks, and redirect output and errors to files.

Learn to manage Linux processes using job controls, nohup, and bg/fg. Monitor with jobs, suspend with ctrl-z, and keep background tasks running after disconnect.

Learn to set up access control lists for files and directories using the setfacl command, adding or revoking permissions for users or groups, and verify with getfacl.

Set up default access control lists with setfacl for directories, applying default acl (not to files), define user, group, and other permissions, and demonstrate inheritance to new files.

Read, modify, and revoke ACL entries using getfacl and setfacl, including -x and -b options for complete removal. Back up recursively with getfacl -R and restore with --set-file backup.

Discover how to remove specific ACLs for a user or group, completely clear ACL entries with setfacl -b, and backup and restore ACLs using getfacl -R and setfacl --restore.

Explore Linux tcp/ip configuration by examining the ETSI configuration files, including hosts, resolv.conf, services, and protocol files, to manage hostnames, IP addresses, DNS servers, and network services.

Explore configuring and inspecting network interfaces using ifconfig and ip commands. Compare their outputs to view IP addresses, netmask, and broadcast, and learn net-tools installation and usage tips.

Analyze ifconfig output to identify loopback and interfaces on Linux, including ip address, netmask, broadcast, mac, and mtu; use ip and route to view routing tables and default gateways.

Configure Linux network interfaces using ifconfig and ip commands under root with sudo, assign IPs with subnet masks, and note changes are not persistent and require netplan.

Explore managing the routing table and default gateway using ip route and route commands; view, delete, and add default gateways, and temporarily change a mac address on an interface.

Configure a static IP with Netplan by creating an ETSI yaml file in the netplan directory, disable the network manager, and apply changes to use the network backend.

Learn to test and troubleshoot network connectivity with the ping utility, including icmp echo requests/replies, ipv4/ipv6 options, reverse dns lookups, and practical gateway-to-public-host checks.

Explore how Linux iptables enables firewalling across IPv4 and IPv6, using chains and rules to accept, drop, or return traffic, with hands-on guidance on syntax, backups, and practice.

View and manage iptables rules with sudo, inspect input, forward, and output chains, and append rules to accept established and related traffic while opening ports 22 and 80 for tcp.

Learn to insert a new rule into the iptables input chain using the insert flag (I), ensuring loopback traffic is allowed for inter-service communication.

Modify the default iptables input policy to drop and append a bottom rule to drop remaining packets, ensuring the loopback and explicit rules remain functional.

Learn how to delete specific iptables rules using the delete option, leverage line numbers to target a rule in the input chain, and observe how deletions shift subsequent rule numbering.

Block and allow traffic with iptables, set a drop policy for outgoing traffic, flush or delete rules, and block domains or IP ranges while accounting for multiple IPs per domain.

Create a user-defined chain named incoming in iptables and attach it to both the input and forward chains to drop traffic from specific source IPs on a given interface.

Discover how the lightweight directory access protocol lets you search for people or resources without knowing their location, and how LDAP uses the directory tree to reveal emails and details.

Learn LDAP basics, terminology, and the directory information tree, including entries, attributes, and object classes, and how they support authentication and centralized user data management.

Learn to create ldif files for ldap directories, using a human readable textual representation to manage distinguished names, domain components, attributes, and object classes for backups and imports.

Explore OpenLDAP, a free open source implementation of the lightweight directory access protocol, covering installation and configuration basics, plus master‑slave replication and ipv6 support.

install OpenLDAP on Ubuntu, install LDAP utils, set the admin password, edit the domain file to corporate.com, reconfigure slapd with updated domain and organization, and complete the setup.

OpenLDAP operations are demonstrated by creating and adding organizational units under corporate.com, using a live file, distinguished names, and simple authentication with the -x option.

Add new users and groups in OpenLDAP by creating user entries with uid, cn, home directory, and shell, and create a group entry using the group object class via ldapadd.

Modify user and group details in LDAP by adding a member to a target group within the finance unit under corporate.com, and validate changes with ldapsearch.

Install and configure phpLDAPAdmin, a web-based LDAP administration tool, and restart Apache to manage LDAP entries and the directory information tree from localhost.

Explore phpLDAPAdmin GUI to manage a Linux LDAP directory, including creating organizational units, users, and groups, using the web interface or command line, and exporting data.