Linux files and folders

Copy and rename, prompt before overwriting
cp -i file dir1/file2
Move and rename
mv file dir1/file2
Recursively delete a folder and its contents
rm -rf /opt/folder/subfolder/
Only remove the contents of a folder
rm -rf /opt/folder/subfolder/*
Show the size of a file or folder
:~# du -hs /opt/tomcat/logs/
825M    /opt/tomcat/logs/
Show disk space used
cd /
du -hs --block-size=M
Show disk space left
cd /
root@debian / # df -TH
Filesystem     Type      Size  Used Avail Use% Mounted on
/dev/md2       ext4      1.1T  866G  162G  85% /
udev           devtmpfs   11M     0   11M   0% /dev
tmpfs          tmpfs     3.4G  345M  3.1G  11% /run
tmpfs          tmpfs     8.4G  8.2k  8.4G   1% /dev/shm
tmpfs          tmpfs     5.3M     0  5.3M   0% /run/lock
tmpfs          tmpfs     8.4G     0  8.4G   0% /sys/fs/cgroup
/dev/md3       ext4      1.9T  1.4T  466G  74% /home
/dev/md1       ext3      512M   55M  431M  12% /boot
Download a file from the internet
wget  -P /target/folder
Pack and unpack a folder
Pack folder
tar -czf archive.tar.gz folder/
Unpack archive
tar -xzf archive.tar.gz
Unpack archive to target
tar -xzf /opt/tmp/archive.tar.gz -C /opt/target/
Monitor log files live
tail -f -n50 error.log

Use -f for live output and -n50 to only print the last 50 lines.