cat /etc/issue :-

The above command gives useful information about Linux distribution and version. There are so many distributions available like RedHat?, Debian, Ubuntu etc.

ifconfig

This is the common command everybody execute to know the IP address of the system along with other network related information. The inet addr key speaks about IP address. This command resides in /sbin and if this is not in path, you have to execute /sbin/ifconfig command.

free -m

The free command shows details about memory usage, free memory available etc. It provides details about memory used for buffering, caching etc and also information about swap space. Swap space is disk area allocated for memory usage in case memory requirement exceeds RAM. buffers/cache is used to store data in memory so that it allows fast access later. Just type free -m and hit enter. -m attribute prints memory details in MB.

df -m
df -h

df command is used to show information regarding available disk space. It prints information regarding mount point, used disk apace, remaining space etc. Type df -m in the command prompt and hit enter. -m attribute shows space in MB.

tar -C path/to/extract/to -xvzf <filename>.tar.gz

Gunzips and untars the file to path/to/extract/to