Introduction — what this is and why it matters for the exam
Unix is a multi-user, multitasking operating system created at Bell Labs in 1969. Linux is a Unix-like, free and open-source operating system whose kernel was released by Linus Torvalds in 1991. Most government and bank servers, web hosting, and networking equipment run Linux/Unix, so almost every OS section of BCS, Bank IT-officer and IT-officer written exams asks about the command line — the text interface where you type commands and the shell (usually bash) executes them.
Exam questions on this topic are highly predictable and factual: "What does chmod 755 mean?", "Which command shows running processes?", "What is the crontab field order?", "What does 2> do?". If you memorize the command tables, the octal-permission arithmetic, and a few worked scripts, this becomes one of the easiest scoring topics in the OS paper. This lesson builds every idea from first principles and gives you the exact tables examiners pull questions from.
Learning objectives
- Compute and read Linux file permissions in both symbolic (
rwx) and octal (755,644) form, and usechmod,chown,chgrp,umask. - Parse an
ls -lline field by field and navigate the filesystem withcd,pwd. - Perform file operations (
cp,mv,rm,mkdir,touch,ln) and explain hard vs symbolic links. - View files with
cat,less,more,head,tail -f. - Search and process text with
grep,find,wc,sort,uniq,cut,awk,sed. - Manage processes with
ps,top,kill,&,jobs,nice. - Schedule jobs with
cron(the 5-field format) andat. - Manage users with
useradd,passwd,sudo,whoami. - Use networking tools
ping,ifconfig/ip,netstat,ssh,scp,wget. - Use pipes and redirection (
|,>,>>,<,2>). - Write basic shell scripts with variables,
if,for,while, exit status, and a shebang.