sudo find /bin/ -user root -perm -4000 -exec ls -ldb {} \; https://www.thegeekdiary.com/understanding-basic-file-permissions-and-ownership-in-linux/

fsck (repair unmount device first)

mkswap (make swap)

resize2fs (resize hard disks) https://askubuntu.com/questions/709716/resize-vm-partition-without-erasing-data

process managermentc

ps -auxf (pid tty stat time command)
ps -AFL (pid ppid lwp c nlwp sz rss psr Stime tty)
ps -AFL –forest (tree hierarchy)
ps -u neko (gets processes of user neko)
ps -p (gets information about process based on process id) ps -Fp (more info about prcoess) ps -p -L -o pid,tid,pcpu,pmem,state,command (all the threads of a process) ps aux | sort -nr -k 3 | head -n 5 (show the top 5 processes that use the most cpu) ps -eo size,pid,user,pcpu,comm --sort cpu | head -n 5 pgrep termite (gets the pid of termite) htop -p

/proc is the folder that every process is a folder. also there is a file for modules and other cool stuff

stat and file are programs to examine files and folders

user/group management

in /etc/shadow
neko:$6$Fl7DFOSWcK1r6i4S$z3WkNoQo1sadwdaddawd/JOHggKzIAoodawdawdsadzGve0GhmjQAFX/:18494:0:99999:7:::
user:$hashtype$hash salt$hash:time since 1970 timeframe to change password:a boolean that enables/disable previous time limit:password expiery(99999 = never):number of days before password expiary that user gets a warning:account:expiary:date:

sudo useradd -m (homepage) -f (days till expiary) -e (expiary date) sudo adduser (has a wizard) sudo passwd (changes password) sudo userdel -r (deletes a user) sudo groupadd (makes a new group) sudo usermod -g (adds user to a group) sudo usermod -G (adds user to multiple groups) sudo usermod -l (changes username)

sudo chage -M 90 -W 7 -I 30 (set a user to have a password expiary of 90 days (-M), gives warning 7 days the expiary (-W), and locks his account after 30 days if inactivity -I) sudo chage -d 0 (set the number of days to change password to 0. so the user has to change password) sudo chage -l (lists the password policy of a user) sudo chage -E0 (expire a user) sudo chage -E-1 (re-enable the user) sudo usermod -L (locks user. authentication failure only) sudo usermod -U (unlock user)

access level:

when you want to add aditional access level to a file or folder, say you want a user to temporary access a file from another users directory you use setfacl to that file.

setfacl -m u:neko:rwx (modifies neko’s access with -m)

sudoers

sudoers file in /etc/sudoers allows you to modify the capability of sudo for each user.
you can add the user “neko” to the sudoers file via adding this to the file:
76 │ ##
77 │ ## User privilege specification
78 │ ##
79 │ root ALL=(ALL) ALL
80 │ neko ALL=(ALL) NOPASSWD:ALL
username allhosts=(all users) nopasswd:allbinaries

show who’s logged in

use w, who, who -a to see who is logged in
last -F | grep -i “still”

list all activity of users

sudo lastb
sudo lastb -s -10min -t -1min (shows last activity of users starting from last 10 minutes up to last minute)
sudo utmpdump /var/log/btmp
sudo utmpdump /var/log/wtmp
/var/log/secure is a log file that logs auhtentication

iprout, ip

ip a (shows interfaces)
ip -4 a show (gives info about a specific interface like eth0) ip link ls up (shows active interfaces) ip -s link (shows statistics about packets) ip a add 10.0.0.10/24 dev (adds ip to that interface) ip a del 10.0.0.10/24 dev (deletes ip from that interface) ip link set down/up (activate/deactivates an interface) ip link set mtu dev (modifies mtu in interface which is the size of largest packet that can be sent over the internet) ip link set txqueuelen dev (modifies qlen which is the buffer size)