Missing manpage for `ifconfig`
Solution 1:
The problem has been resolved by re-installing the "net-tools" package. The possible cause of such issue might be a skewed previous installation.
$ sudo apt-get install --reinstall net-tools
P.S.: At the time during my research for solutions on this issue, I found that I need to know which package the command belongs to. Here is how you do it:
$ dpkg -S `which ifconfig`
Solution 2:
Check the man for other commands. If you face the same problem with all the commands then the reason is that the $MANPATH might not be correctly set.
Please set the $MANPATH by
export $MANPATH=/path/to/man
For example:
export $MANPATH=/usr/local/man:/usr/local/share/man:/usr/share/man