Linux Command Line Reference for System Diagnostics and File Management

Posted on Oct 18, 2025 in Computers

Linux Command Line Reference for System Diagnostics

This reference details essential Linux commands used for system investigation, including checking disk usage, locating files, analyzing file content, and retrieving general system information.

1. Estimating Disk and File Size

du -sh /SOURCE: Estimates the total size of the specified directory or file /SOURCE.
df -h /SOURCE: Provides information on the hard disk partition usage where the file or directory /SOURCE resides.
df -h: Lists all hard disk partitions and displays their sizes and usage statistics in human-readable format.

2. Locating Files and Commands

which EXECUTABLE: Determines if the specified EXECUTABLE (program name) is installed, located in the system’s PATH, and shows its full path.
whereis PROGRAM: Determines the locations of the binary, source, and manual (man) files for the specified PROGRAM.
whatis COMMAND: Displays a brief description of the specified COMMAND.
find /SOURCE -name 'NAME': Prints to the screen the path if a file named NAME is found within the directory /SOURCE.
find /SOURCE -name '*pattern*': Prints to the screen all files containing the specified pattern in their name within the directory /SOURCE.
find . -name '*PATTERN*': Prints to the screen all files containing the specified PATTERN in their name, starting from the current directory and traversing the directory tree.
slocate -r PATTERN: Searches the locate database and prints all files containing the text PATTERN in their name. Access to the database may require root privileges.
apropos PATTERN: Searches the whatis database and prints all entries that include the specified PATTERN.

3. Investigating File Content and Attributes

3.1. File Type and Listing

file /SOURCE: Determines and prints the file type to the display.
ls -l /SOURCE: Lists the contents of /SOURCE, displaying detailed information including permissions, size, and modification date of files.
ls -l /SOURCE | less: Lists the contents of /SOURCE. The output is piped (|) to less for paged viewing, useful when the list is too long for the console.
less /SOURCE: Prints the content of the file /SOURCE to the screen, allowing for paged viewing.

3.2. Searching File Content (Grep)

grep -i 'PATTERN' /SOURCE: Searches inside the file /SOURCE for lines matching the text PATTERN (case-insensitive, -i) and prints the full matching lines to the screen.
grep -Ri 'PATTERN' /SOURCE: Searches recursively (-R) in the directory /SOURCE (and its subdirectories) for lines matching the PATTERN (case-insensitive, -i). Prints the file name and the corresponding matching lines.
grep -Ri 'PATTERN' /SOURCE | less: Searches recursively in the directory /SOURCE for lines matching the PATTERN. The output is piped (|) to less for paged viewing.

4. Retrieving General System Information

who -b: Displays the date and time the system was last booted.
who -r: Displays the current system runlevel.
whoami: Displays the effective username of the current user.
uname -r: Displays the version of the running kernel.
arch: Prints the machine architecture to the screen.
lspci: Provides detailed information about all PCI devices.
id: Prints the user identification number (UID) and current group identification numbers (GIDs).
pwd: Prints the current working directory.
printenv: Prints all environment variables.
dmesg: Prints the last messages generated by the kernel buffer to the screen.
dmesg | grep -i 'error': Filters the kernel messages (dmesg) and prints only those lines containing the text ‘error’ (case-insensitive).
ps: Prints the identification numbers (PIDs) of running processes.
top: Provides comprehensive, real-time information on system status, processes, CPU usage, and memory.
cat /proc/cpuinfo: Provides detailed information about the processor(s).
cat /proc/mounts: Provides information on partitions or network resources currently mounted on the machine.
alias: Lists all defined command aliases.
lsmod: Lists all modules currently loaded into the kernel, along with additional information. May require root privileges.
free: Lists the amount of used and available physical RAM and swap memory.
history: Lists the commands previously executed by the user.
manpath: Prints the search path for manual (man) pages.
mount: Lists all currently mounted devices in the system.
type COMMAND: Provides the location of the executable COMMAND and indicates whether it is an alias, function, or built-in shell command.
toe: Lists available terminal types.
set: Lists all defined shell variables and functions.
whoami: Displays the current user. This command produces the same result regardless of arguments used.