userfull of commands
# current directory
pwd
# shutdown
shutdown -h now
# print lines matching a pattern - grep
grep something_you_like_to_find file.txt
# special characters in the grep command
getsebool -a | grep -e '--> on'
# redo last command but as root
sudo !!
# open an editor to run a command
ctrl+x+e
# create a super fast ram disk
mkdir -p /mnt/ram
mount -t tmpfs tmpfs /mnt/ram -o size=8192M
# fix a really long command that you messed up
fc
# tunnel with ssh (local port 3337 -> remote host's 127.0.0.1 on port 3389)
ssh -L 3337:127.0.0.1:3389 root@some.fi -N
# quickly create folders
mkdir -p folder/{sub1,sub2}/{sub1,sub2,sub3}
# intercept stdout and log to file
cat file | tee -a log | cat > /dev/null
# exit terminal but leave all processes running
disown -a && exit
# check if some port is open
nc -zv www.google.com 443
Connection to www.google.fi port 443 [tcp/https] succeeded!#
echo >/dev/tcp/www.google.com/443 &>/dev/null && echo "open" || echo "close"
open
# size of each folder (only folder size)
du -h --max-depth=1 /var
208K /var/tmp
233M /var/lib
152M /var/log
0 /var/adm
1.5G /var/cache
12K /var/db
0 /var/empty
0 /var/games
0 /var/gopher
0 /var/local
0 /var/nis
0 /var/opt
0 /var/preserve
1.6M /var/spool
0 /var/yp
0 /var/kerberos
0 /var/crash
0 /var/account
1.9G /var
# permanently remove file securely
-z – adds a final overwrite with zeros to hide shredding
-v – enables display of operation progress
-u – truncates and removes file after overwriting
-n – specifies number of times to overwrite file content (the default is 3)
$ shred -zvu -n 10 filename.txt
# refresh environment variables
source filename [options]
#
watch ls -lhs
watch -d free -m
tail -f /var/log/messages
# add user oneliner
useradd -G wheel,sshallowed -c "Comment" username && passwd username
Permissions:
chmod xxx file | Directory
Start at 0
read permission should be set, add 4
write permission should be set, add 2
execute permission should be set, add 1
https://www.redhat.com/sysadmin/suid-sgid-sticky-bit