Pro Linux System Administration

gistfile1.sh

=users and groups
# add user into 'admin' group, only users in 'admin' group can use 'sudo'
sudo usermod -G admin username
# useradd defaults
/etc/default/useradd
# check to what groups user belongs to
id username

# ubuntu
adduser, addgroup
# change password
passwd
# set password expirations for 30 days
sudo chage -M 30 ataylor

# disable user
sudo usermod ­-­-expiredate 1

# copy contents of the folder to another folder
sudo cp -R * /var/lib/tomcat6/lib/

# login as another user
su {username}
#check who is listening on particular port
netstat -lnp | grep :80


# make vpn connection last long
sudo vpnc --dpd-idle 0

# find all files modified 90 min ago
find . -mmin -90

# find all files in particular directory by some extension
# and add execution permission for all users for those files
find ./application/default/cmd/ -name "*.php" | xargs chmod a+x

# imitate slow connection, i.e. 2 sec delay between each pocket sent
sudo tc qdisc change dev eth0 root netem delay 2000ms

# edit crontab with vim
env EDITOR=vim crontab -e

# check which files are opened by particular process
/usr/sbin/lsof -p 9537

# scan local network
nmap -sP 192.168.1.0/24

# restore MySQL database from raw backup
cp -R /old_file_system/var/lib/mysql/* /var/lib/mysql

# rsync from remote through ssh
rsync -avz -e ssh remoteuser@remotehost:/remote/dir /this/dir/

## single file
rsync -chavzP --stats user@remote.host:/file/path.json /file/path.json 

# get total occupied disk space by the directory
du -ch /path/to/directory | grep total

# inspect disk usage
df -h