System Information
Understanding your system's hardware and software configuration
uname -a # Displays kernel version and system architecture. lscpu # Provides detailed information about the CPU. lsblk # Lists all available block devices. lsusb # Shows USB devices connected to the system.
CPU and Memory Diagnostics
Monitoring CPU and memory usage helps in identifying performance bottlenecks.
Commands:
htop is an interactive system monitor process viewer and process manager. It is designed as an alternative to the Unix program top. It shows a frequently updated list of the processes running on a computer, normally ordered by the amount of CPU usage.
htop
vmstat -s Provides a detailed breakdown of memory usage and other related metrics since the last system boot.
vmstat -s
980492 K total memory
480208 K used memory
132040 K active memory
582364 K inactive memory
67924 K free memory
21724 K buffer memory
410636 K swap cache
0 K total swap
0 K used swap
0 K free swap
free -h Displays memory usage in "human-readable" format
free -h
total used free shared buff/cache available
Mem: 7.7G 1.9G 3.9G 487M 1.9G 5.0G
Swap: 2.0G 0B 2.0G
Disk Usage and Health
Keeping track of disk usage and health is crucial for preventing data loss and ensuring efficient storage management.
df -h # Shows disk space usage in "human-readable" format
df -h Filesystem Size Used Avail Use% Mounted on udev 3.8G 0 3.8G 0% /dev tmpfs 783M 1.7M 781M 1% /run /dev/sda2 233G 25G 197G 12% / tmpfs 3.9G 39M 3.8G 1% /dev/shm tmpfs 5.0M 4.0K 5.0M 1% /run/lock tmpfs 783M 80K 783M 1% /run/user/1000
du -sh /path/to/directory Displays the size of a specific directory.
du -sh /path/to/directory 1.1G /path/to/director iostat # Reports CPU and I/O statistics.
fdisk -l # List all partitions
fdisk -l Disk /dev/sda: 20 GiB, 21474836480 bytes, 41943040 sectors Disk model: QEMU HARDDISK Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt Disk identifier: XXXXXX-XXX-XXX-XXXX-XXXXXXXXXX Device Start End Sectors Size Type /dev/sda1 2048 4095 2048 1M BIOS boot /dev/sda2 4096 41940607 41936512 20G Linux filesystem
Process and Service Management
Managing processes and services is essential for maintaining system stability.
ps aux # Lists all running processes
ps aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.0 168800 10944 ? Ss Jun12 0:02 /sbin/init root 2 0.0 0.0 0 0 ? S Jun12 0:00 [kthreadd] root 3 0.0 0.0 0 0 ? I< Jun12 0:00 [rcu_gp] root 4 0.0 0.0 0 0 ? I< Jun12 0:00 [rcu_par_gp] ...
systemctl status service_name # Checks the status of a service
systemctl status apache2
● apache2.service - The Apache HTTP Server
Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2024-05-29 16:06:04 UTC; 2 weeks 5 days ago
Docs: https://httpd.apache.org/docs/2.4/
Process: 1000205 ExecReload=/usr/sbin/apachectl graceful (code=exited, status=0/SUCCESS)
Main PID: 40385 (apache2)
Tasks: 55 (limit: 1013)
Memory: 8.8M
CPU: 1min 55.654s
CGroup: /system.slice/apache2.service
├─ 40385 /usr/sbin/apache2 -k start
├─1000209 /usr/sbin/apache2 -k start
└─1000210 /usr/sbin/apache2 -k start
kill -9 process_id(PID) # Forces termination of a process. (No output unless there is an error, the process is terminated forcefully)
Logs and Monitoring
Analyzing logs and monitoring system activities can help in identifying issues and tracking system performance.
dmesg # allows reviewing messages stored in the Linux ring buffer, providing insights into hardware errors and startup issues. How To Use dmesg
dmesg -T [Wed May 29 14:46:00 2024] Run /init as init process [Wed May 29 14:46:00 2024] with arguments: [Wed May 29 14:46:00 2024] /init [Wed May 29 14:46:00 2024] with environment: [Wed May 29 14:46:00 2024] HOME=/ [Wed May 29 14:46:00 2024] TERM=linux [Wed May 29 14:46:00 2024] BOOT_IMAGE=/boot/vmlinuz-5.15.0-97-generic [Wed May 29 14:46:00 2024] biosdevname=0 [Wed May 29 14:46:00 2024] netcfg/do_not_use_netplan=true [Wed May 29 14:46:00 2024] piix4_smbus 0000:00:01.3: SMBus Host Controller at 0x700, revision 0 [Wed May 29 14:46:00 2024] scsi host2: Virtio SCSI HBA [Wed May 29 14:46:00 2024] scsi 2:0:0:0: Direct-Access QEMU QEMU HARDDISK 2.5+ PQ: 0 ANSI: 5 [Wed May 29 14:46:00 2024] input: VirtualPS/2 VMware VMMouse as /devices/platform/i8042/serio1/input/input4 [Wed May 29 14:46:00 2024] input: VirtualPS/2 VMware VMMouse as /devices/platform/i8042/serio1/input/input3 [Wed May 29 14:46:00 2024] cryptd: max_cpu_qlen set to 1000
journalctl # Views systemd logs and allows filtering Linux system logs to extract relevant information for monitoring and troubleshooting. How To Use journalctl
journalctl -- Logs begin at Tue 2024-06-18 10:55:23 UTC, end at Tue 2024-06-18 12:06:19 UTC. -- Jun 18 10:55:23 hostname kernel: Linux version 5.4.0-74-generic (buildd@lcy01-amd64-013) (gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)) #83-Ubuntu SMP Thu May 6 10:34:06 UTC 2021 (Ubuntu 5.4.0-74.83-generic 5.4.101) Jun 18 10:55:23 hostname kernel: Command line: BOOT_IMAGE=/boot/vmlinuz-5.4.0-74-generic root=UUID=5d7f5dcd-1234-5678-9abc-def012345678 ro quiet splash vt.handoff=7 ...
journalctl -u service_name # Views Logs for a Specific Service
journalctl -u apache2 -- Logs begin at Tue 2024-06-18 10:55:23 UTC, end at Tue 2024-06-18 12:05:19 UTC. -- Jun 18 11:56:19 hostname systemd[1]: Starting The Apache HTTP Server... Jun 18 11:56:19 hostname apache2[1342]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' directive globally to suppress this message Jun 18 11:56:19 hostname systemd[1]: Started The Apache HTTP Server.