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westenfelder

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show the free space on all filesystems

df -h

lists the name and pids of the top 5 processes by percentage of CPU usage

ps -eo pid,comm,%cpu --sort=-%cpu | head -n 6

shows how much free memory a system has

free -h

shows how much free space there is on the root filesystem

df -h /

shows the disk space used by the directory /var/log

du -sh /var/log

show the last date and time the system was rebooted

who -b

show how long the system has been up

uptime -p

who is currently logged into the system

who

install wget on Redhat without user input

yum install -y wget

set my user's time zone to Los Angeles

timedatectl set-timezone America/Los_Angeles

show the version of the kernel

uname -r

show the version of the operating system

cat /etc/os-release

find the largest file under my home directory

find ~ -type f -exec ls -lh {} + | sort -k 5 -hr | head -n 1

make data.dat readable by just the owner

chmod 400 data.dat

set the file creation mask so that only the owner has file write permission

umask 037

create a new file called data.dat with a size of 512K bytes

truncate -s 512K data.dat

create an ext3 filesystem in my existing file named disk.img

mkfs.ext3 disk.img

set the system's timezone to Los Angeles

timedatectl set-timezone America/Los_Angeles

create a new group called alfa

groupadd alfa

add user test to the group called alfa

usermod -aG alfa test

add user test to the alfa group as administrator

usermod -aG alfa test; gpasswd -A test alfa

remove the group password from the alfa group

gpasswd -r alfa

restrict access of all users in the group named alfa

chmod -R o-rwx /path/to/directory

remove user test from the alfa group

gpasswd -d test alfa

remove the alfa group

groupdel alfa

add a new user named test

adduser test

add a login for a new user named test which expires 90 days from today

useradd -e $(date -d "+90 days" +%Y-%m-%d) test

give me the date 90 days from today

date -d "+90 days"

create a new systems group called alfa2

groupadd alfa2

lock user test2's account

usermod -L test2

force user test2 to change their password at next login

chage -d 0 test2

modify the access time of my file data.dat to be 12:00 on 2022-12-31

touch -a -t 202212311200 data.dat

create a FIFO named myfifo in /tmp

mkfifo /tmp/myfifo

insert #!/usr/bin/python3 at the top of each *.py files under the current directory

for file in *.py; do sed -i '1i #!/usr/bin/python3' "$file"; done

rename all of my files named test.py replacing the string test with unit_test

find . -type f -name 'test.py' -execdir mv {} unit_test.py \;

prefix every non-blank line in file.log with the string 'hello'

sed '/./ s/^/hello/' file.log

change the file extension from .mpg to .avi every file in directory /home/test/uploads

for file in /home/test/uploads/*.mpg; do mv "$file" "${file%.mpg}.avi"; done

prefix the line number to every line in file.log

nl -ba file.log

make the file pretty-print.sh executable

chmod +x pretty-print.sh

append all PNG and JPG files to the existing tar archive file images.tar

tar -rf images.tar *.png *.jpg

calculate the md5 checksum of every file under the directory named downloads

find downloads -type f -exec md5sum {} +

change the group ownership to alfa of my file named download.dat

chgrp alfa download.dat

count all of the directories under my home directory

find ~ -type d | wc -l

list the *.dat files in the current directory in ascending order by size

ls -lS --block-size=1 --reverse *.dat

create the path src/vpd/new without an error if the path already exists

mkdir -p src/vpd/new

list all files in my Downloads directory which have not been accessed within the last 3 weeks

find ~/Downloads -type f -atime +21

count the total number of lines in the *.c files under my src directory

find src -name "*.c" -type f -exec wc -l {} + | awk '{total += $1} END {print total}'

find all *.c and *.h files under the src directory containing the pattern TODO and print just the file names

grep -lR "TODO" src --include \*.c --include \*.h

show the fully-qualified domain name of my host

hostname -f

calculate the number of days between the dates Jan 12, 2023 and Jan 20, 2024

echo $(( ($(date -d "Jan 20, 2024" +%s) - $(date -d "Jan 12, 2023" +%s)) / 86400 ))