Linux File Viewing, Permissions, and Environment Variables¶

← Back to Linux Commands

This section covers file viewing commands, Linux permissions, ownership, and environment variables — all heavily used by DevOps engineers for log analysis, access control, and runtime debugging.

`head` – View First Lines of a File¶

Prints the first 10 lines of a file by default.

[opc@new-k8s ~]$ head fruits.txt
Apple
Apricot
Avocado
Banana
Bilberry
Blackberry
Blackcurrant
Blueberry
Boysenberry
Currant

View First N Lines¶

[opc@new-k8s ~]$ head -n 15 fruits.txt
Apple
Apricot
Avocado
Banana
Bilberry
Blackberry
Blackcurrant
Blueberry
Boysenberry
Currant
Cherry
Cherimoya
Chico fruit
Cloudberry
Coconut

`tail` – View Last Lines of a File¶

Prints the last 10 lines of a file by default.

[opc@new-k8s ~]$ tail fruits.txt
Salak
Satsuma
Soursop
Star fruit
Solanum quitoense
Strawberry
Tamarillo
Tamarind
Ugli fruit
Yuzu

View Last N Lines¶

[opc@new-k8s ~]$ tail -n 15 fruits.txt
Raspberry
Salmonberry
Rambutan
Redcurrant
Salal berry
Salak
Satsuma
Soursop
Star fruit
Solanum quitoense
Strawberry
Tamarillo
Tamarind
Ugli fruit
Yuzu

Linux File Permissions Explained¶

----------
drwxrwxrwx

-  → file
d  → directory
l  → link

r → read  (4)
w → write (2)
x → execute (1)

Owner | Group | Others

Changing File Permissions Using `chmod`¶

Give Read & Write Permission to User Only¶

[opc@new-k8s ~]$ chmod 600 random.txt
[opc@new-k8s ~]$ ll
-rw-------. 1 opc opc 0 Apr 15 04:19 random.txt

Give Read & Write Permission to User and Group¶

[opc@new-k8s ~]$ chmod 660 random.txt
[opc@new-k8s ~]$ ll
-rw-rw----. 1 opc opc 0 Apr 15 04:19 random.txt

Changing File Owner and Group (`chown`)¶

[opc@new-k8s ~]$ sudo chown opc:vignesh random.txt
[opc@new-k8s ~]$ ll
-rw-rw----. 1 opc vignesh 0 Apr 15 04:19 random.txt

Changing Group of a Directory and All Files Recursively¶

[opc@new-k8s ~]$ sudo chown -R opc:vignesh test/

[opc@new-k8s ~]$ ll
drwxrwxr-x. 4 opc vignesh 100 Apr 13 12:46 test

`date` – Check Date and Time¶

[opc@new-k8s test]$ date
Sat Apr 15 04:39:46 GMT 2023

Environment Variables¶

View All Environment Variables Using `env`¶

[opc@new-k8s test]$ env
HOSTNAME=new-k8s
USER=opc
PWD=/home/opc/test
PATH=/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/opc/.local/bin:/home/opc/bin
...

View All Environment Variables Using `printenv`¶

[opc@new-k8s test]$ printenv
HOSTNAME=new-k8s
USER=opc
PWD=/home/opc/test
PATH=/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/opc/.local/bin:/home/opc/bin
...

View a Single Environment Variable¶

[opc@new-k8s test]$ echo $PATH
/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/opc/.local/bin:/home/opc/bin

Practice Tasks¶

Use head and tail to inspect a file
Change permissions of a file to 600 and 660
Change ownership of a file using chown
Print all environment variables
Print only the PATH variable

🧠 Quick Quiz — File Permissions & Environment Variables¶

#

Which permission value represents read and write access for the file owner only?

📝 Want More Practice?¶

To strengthen your understanding and prepare for interviews, try the full 20-question practice quiz based on this chapter:

👉 Start File Permissions & Environment Variables Quiz (20 Questions)

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