The df command is useful in reporting disk space usage.  However, recently encountered a system that would hang after issuing the df command.  A CTL-C or CTL-Z would not escape this annoyance.  The issue was quickly resolved by reinstalling stystemd.

yum -y reinstall systemd

After reinstalling systemd, the df command was reissued and was quite responsive.

Source

https://serverfault.com/questions/911811/centos-7-df-started-to-hang