Generic and useful commands

List crontab content of all user:

for user in $(cut -f1 -d: /etc/passwd); do crontab -u $user -l; done

DNS

• dig domain.tld
• dig @ns.server.tld domain.tld: ask ns.server.tld to know domain.tld dns informations
• dig -x XXX.XXX.XXX.XXX: domain reverse

Network

• netstat -atnpu: port stats

Mysql

• echo "CREATE DATABASE databasename" | mysql -u username -p: Create new database

• mysqldump -u root --password="password" --all-databases | gzip> all_databases_dump.sql.gz: Dump all Mysql databases

• mysql < dump.sql: Resore databases from a sql file

• mysql database_name < dump.sql: Resore a database from a sql file

PostgreSQL

• pg_dump -U <username> -Fc --file=database.dump <database>

Users/groups

• adduser --groups group_name user_name: Create user
• adduser --system --no-create-home [--disabled-password] [--disabled-login] [--shell /bin/bash] --home-dir / --groups group_name user_name: Create system user

• adduser user_name group_name: Add a user into a group

• deluser user_name: Remove a user

• deluser user_name group_name: Remove a user from a group

Get data from an other server

Run this command from on new server.
ssh remote.srv.tld "cd /data/;tar zcf - files" | tar zxf -
This command recursively copies /data/files from remote.srv.tld to local server a lot faster on slow network.

Source

Regular synchronization

# --delete: remove files they are in remote but not in source

# r: recursive
# a: archive
# z: compression
# e: protocol `ssh`

# source destination

rsync --delete -raze "ssh" remote.server.tld:/path/to/rsync/ /path/to/rsync/

Disk and sizes

• du -hs /path/to/folder: Get folder size

• df -h: Get disks size

• find /folder -type f -size +1048576 -exec ls -lh {} \;: Search files size greater than 1G

Others

• iptables -L -n -v

• su user_name -c 'command to execute': execute a command with user_name user

• ssh -f remote.server.tld -L local_port:localhost:remote_port -N: open an ssh tunnel

• find /folder -name ".svn" -exec rm -rf {} \;: remove .svn directories into /folder

• find /folder -type l -exec ls -lad {} \;: find symlinks into /folder

• tar cfz archive.tar.gz target_dir_or_file: archive and compress file or directory into tar.gz

• tar xfz archive.tar.gz /path/to/unarchive: unarchive a tar.gz file

Tools

• rkhuntuer: root kit hunter