Search the Community

1. sudo – Execute commands with elevated privileges, a fundamental for system administration. 2. useradd – Create a new user account, essential for managing user access. 3. usermod – Modify a user account, useful for changing account properties. 4. userdel – Delete a user account, important for managing system access. 5. groupadd – Add a new group, crucial for managing group permissions. 6. groupmod – Modify a group, allows changing group attributes. 7. groupdel – Delete a group, used for removing group access. 8. chown – Change file owner and group, vital for managing file permissions. 9. chmod – Change file access permissions, key for securing system files. 10. chgrp – Change group ownership, important for managing group file access. 11. passwd – Update a user’s password, critical for account security. 12. adduser – Add a user account (more interactive than useradd). 13. deluser – Delete a user account (more user-friendly than userdel). 14. visudo – Edit the sudoers file, crucial for configuring sudo privileges. 15. systemctl – Control and manage systemd units, essential for managing services. # 1. Start a service immediately systemctl start serviceName.service # 2. Stop a service immediately systemctl stop serviceName.service # 3. Restart a service systemctl restart serviceName.service # 4. Show the status of a service systemctl status serviceName.service # 5. Enable a service to start on boot systemctl enable serviceName.service # 6. Disable a service from starting on boot systemctl disable serviceName.service # 7. Check whether a service is enabled systemctl is-enabled serviceName.service # 8. Reload the service configuration without interrupting operations systemctl reload serviceName.service # 9. View all running services systemctl list-units --type=service --state=running # 10. Mask a service to prevent it from being started, manually or automatically systemctl mask serviceName.service 16. journalctl – Query and display messages from the journal, used for system logging. # 1. Display all log messages journalctl # 2. Display log messages from the current boot journalctl -b # 3. Display log messages from a previous boot journalctl -b -1 # 4. Follow the journal live (similar to tail -f) journalctl -f # 5. Show kernel messages (similar to dmesg) journalctl -k # 6. Filter log messages by a specific unit journalctl -u nginx.service # 7. Filter log messages by priority (0=emerg to 7=debug) journalctl -p err # 8. Show log messages in a specific time range journalctl --since "2023-01-01" --until "2023-01-02" # 9. Show log messages for a specific process ID journalctl _PID=1234 # 10. Combine filters, e.g., show error messages for a specific unit since yesterday journalctl -u apache2.service -p err --since yesterday 17. top – Display task manager, important for monitoring system performance. # Note: Most examples are intended to be used within top's interactive mode # 1. Start top with a specific delay between updates in seconds top -d 5 # 2. Display top for a specific user's processes top -u username 18. htop – Interactive process viewer, an enhanced alternative to top. 19. df – Report file system disk space usage, crucial for monitoring disk usage. 20. du – Estimate file space usage, useful for managing disk space. 21. free – Display memory usage, important for memory management. 22. vmstat – Report virtual memory statistics, helpful for performance monitoring. # 1. Basic usage - Display virtual memory statistics vmstat # 2. Display vmstat output with a specific interval and count # This will display the report every 2 seconds, 5 times vmstat 2 5 # 3. Show memory statistics in megabytes vmstat -S M # 4. Display additional information including slab info vmstat -m # 5. Display disk statistics vmstat -d # 6. Display partition statistics vmstat -p /dev/sda1 # 7. Display event counter statistics vmstat -s # 8. Show CPU activity as an average since the last reboot vmstat -a # 9. Include timestamps in the output vmstat -t # 10. Display statistics with a delay and include timestamp # This will show the report every 3 seconds with the timestamp included vmstat 3 -t 23. iostat – Monitor system input/output device loading, used for diagnosing performance issues. # 1. Basic usage - Display the CPU and device utilization report iostat # 2. Display the report at 2-second intervals iostat 2 # 3. Display the extended statistics with more details iostat -x # 4. Display disk utilization report every 2 seconds, 3 times iostat 2 3 # 5. Show only CPU statistics iostat -c # 6. Show only device utilization statistics iostat -d # 7. Display statistics in megabytes per second iostat -m # 8. Show extended statistics with device utilization, refreshing every 5 seconds indefinitely iostat -dx 5 # 9. Display statistics for a specific device (e.g., sda) iostat -d sda # 10. Display persistent device names and extended statistics iostat -Nx 24. netstat – Display network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. # 1. List all ports (both listening and non-listening ports) netstat -a # 2. List all listening ports netstat -l # 3. Display TCP connections netstat -t # 4. Display UDP connections netstat -u # 5. Show statistics by protocol (e.g., TCP, UDP) netstat -s # 6. Display listening TCP ports with numeric addresses and don't resolve names netstat -lnt # 7. Display listening UDP ports with numeric addresses and don't resolve names netstat -lnu # 8. Show the routing table netstat -r # 9. Display all sockets, including listening and non-listening, without resolving names netstat -an # 10. Show which process is using a particular port netstat -tulnp 25. ss – Another utility to investigate sockets, replaces netstat. 26. ip – Show / manipulate routing, devices, policy routing and tunnels, central for network configuration. 27. ifconfig – Configure a network interface, traditionally used before ip. 28. iptables – Administer IPv4 packet filtering and NAT, key for firewall management. # 1. List all current iptables rules iptables -L # 2. Block traffic from a specific IP address iptables -A INPUT -s 192.168.1.100 -j DROP # 3. Allow SSH access from a specific IP address iptables -A INPUT -p tcp -s 192.168.1.100 --dport 22 -j ACCEPT # 4. Reject all incoming traffic but allow outgoing traffic iptables -P INPUT REJECT iptables -P OUTPUT ACCEPT # 5. Allow traffic to a specific port (e.g., HTTP port 80) iptables -A INPUT -p tcp --dport 80 -j ACCEPT # 6. Delete all rules in a specific chain (e.g., INPUT chain) iptables -F INPUT # 7. Block all traffic from a specific subnet iptables -A INPUT -s 192.168.1.0/24 -j DROP # 8. Allow all incoming traffic on a specific interface (e.g., eth0) iptables -A INPUT -i eth0 -j ACCEPT # 9. Log dropped packets iptables -A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables dropped: " --log-level 7 # 10. Save iptables rules to be loaded on boot iptables-save > /etc/iptables/rules.v4 29. firewalld – Dynamically manage firewall with support for network zones. # 1. Start firewalld sudo systemctl start firewalld # 2. Enable firewalld to start at boot sudo systemctl enable firewalld # 3. Check the status of firewalld sudo systemctl status firewalld # 4. Reload firewalld rules without losing state sudo firewall-cmd --reload # 5. List all active zones sudo firewall-cmd --get-active-zones # 6. Set the default zone sudo firewall-cmd --set-default-zone=public # 7. Add a service to the default zone permanently sudo firewall-cmd --permanent --add-service=http # 8. Open a port in the default zone permanently sudo firewall-cmd --permanent --add-port=8080/tcp # 9. Remove a service from the default zone permanently sudo firewall-cmd --permanent --remove-service=http # 10. List all rules in the default zone sudo firewall-cmd --list-all 30. nftables – Modern replacement for iptables, ip6tables, arptables, and ebtables. 31. crontab – Schedule periodic background jobs, essential for automating tasks. 32. rsync – Fast, versatile file copying tool, important for backups and synchronization. 33. tar – Archive utility, used for packing and unpacking archive files. 34. gzip / bzip2 – Compress or expand files, crucial for managing file sizes. 35. unzip / zip – Compress and decompress files in zip format. 36. mount – Mount a filesystem, important for attaching storage devices. 37. umount – Unmount file systems, counterpart to mount. 38. fsck – Check and repair a Linux filesystem, crucial for filesystem maintenance. 39. lvm – Logical Volume Manager, essential for managing disk storage. 40. ssh – Secure Shell, a protocol for secure remote login and other secure network services. 41. scp – Secure copy (remote file copy program), used for secure file transfer. 42. sftp – Secure File Transfer Program, another secure file transfer utility. 43. wget – Non-interactive network downloader, used for downloading files from the web. 44. curl – Tool to transfer data from or to a server, supports various protocols. # 1. Download a file curl -O http://example.com/file.txt # 2. Save the downloaded file with a specific filename curl -o newfilename.txt http://example.com/file.txt # 3. Use curl with a user agent curl -A "Mozilla/5.0" http://example.com # 4. Send a GET request curl -X GET http://example.com # 5. Send a POST request with data curl -X POST -d "data=example" http://example.com/post # 6. Send a POST request with a file curl -X POST -F "file=@localfile.txt" http://example.com/upload # 7. Pass a header to the HTTP request curl -H "X-Custom-Header: value" http://example.com # 8. Follow HTTP redirects curl -L http://example.com # 9. Perform a basic HTTP authentication curl -u username:password http://example.com # 10. Use verbose mode to see request/response details curl -v http://example.com # 11. Make a request to an HTTPS site that has a self-signed cert curl -k https://example.com # 12. Resume a previous file transfer curl -C - -O http://example.com/bigfile.zip # 13. Limit the bandwidth for file download curl --limit-rate 100K -O http://example.com/bigfile.zip # 14. Use a proxy for the HTTP request curl -x http://proxy-server:port http://example.com # 15. Get the HTTP headers of a URL curl -I http://example.com # 16. Use cookies with your request curl -b "name=value" http://example.com # 17. Store server's response cookies into a file curl -c cookies.txt http://example.com # 18. Send a custom request method curl -X PUT http://example.com # 19. Use IPv6 for the request curl -6 http://example.com # 20. Include both request headers and response in the output curl -i http://example.com The post Linux Tutorials: Commands for Linux Administrator appeared first on DevOpsSchool.com. View the full article

A brief introduction to Ansible roles for Linux system administration In this part one of two articles, learn to use rhel-system-roles with your Ansible deployment to better manage functionality such as network, firewall, SELinux, and more on your Red Hat Enterprise Linux servers. Shiwani Biradar Mon, 1/18/2021 at 2:07pm Image Photo by RODNAE Productions from Pexels Ansible is an open source automation platform that includes configuration management, application deployment, and infrastructure orchestration. It is a popular automation tool for DevOps engineers and for system administrators. System administrators often face career burnout due to long hours and from performing repetitive tasks on many systems, but Ansible helps make these tasks easier to complete. Tasks such as user creation, service management, and software installs can be accomplished using Ansible. Topics: Linux Linux Administration Ansible Read More at Enable Sysadmin The post A brief introduction to Ansible roles for Linux system administration appeared first on Linux.com. View the full article