Quiz: Linux Fundamentals

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5 questions

L0 (3 questions)

1. What does chmod 755 script.sh do?

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Sets owner read/write/execute (7), group read/execute (5), others read/execute (5). Owner can modify, everyone can run. *Common mistake:* Many people confuse the octal digits. 7=rwx, 6=rw-, 5=r-x, 4=r--.

2. How do you find which process is using port 8080?

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ss -tlnp | grep 8080 or lsof -i :8080. ss is preferred on modern systems.

3. What is the difference between a hard link and a soft link?

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Hard link points to the same inode (same data, survives original deletion). Soft link (symlink) points to a path (breaks if target deleted).

L1 (1 questions)

1. What useful information is in /proc and how do you read it?

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/proc is a virtual filesystem exposing kernel and process state. Key entries: /proc/PID/status (process memory, state), /proc/PID/fd/ (open file descriptors), /proc/cpuinfo (CPU details), /proc/meminfo (memory breakdown), /proc/loadavg (load averages), /proc/mounts (mounted filesystems), /proc/net/tcp (open sockets). Read with cat — these are pseudo-files generated on demand. /proc/PID/environ shows process environment variables.

L2 (1 questions)

1. How does the Linux virtual memory system work and what happens when RAM is full?

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Linux uses virtual memory with demand paging. Each process gets a virtual address space; pages are loaded into physical RAM on first access (page fault). The kernel maintains page cache (file data), anonymous pages (heap/stack), and mapped pages. When RAM is full:
1. Kernel reclaims page cache (safe — can re-read from disk).
2. Swaps anonymous pages to swap space (slow).
3. If still insufficient, the OOM killer activates. Check: free -h (available includes reclaimable cache), /proc/meminfo (detailed breakdown), vmstat (swap in/out rates).