tmpfs: command not found

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I'm trying to run the following command

[root@fedora bruno]# tmpfs /opt/jdk tmpfs defaults,mode=1777 0 0

But a get this output

bash: tmpfs: command not found

To me its odd becouse of this

root@fedora bruno]#  df -h
Sist. Arq.               Tam. Usado Disp. Uso% Montado em
devtmpfs                 1,9G     0  1,9G   0% /dev
tmpfs                    1,9G     0  1,9G   0% /dev/shm
tmpfs                    1,9G  1,3M  1,9G   1% /run
tmpfs                    1,9G     0  1,9G   0% /sys/fs/cgroup
/dev/mapper/fedora-root   50G  8,0G   39G  18% /
tmpfs                    1,9G   28K  1,9G   1% /tmp
/dev/sda1                976M  174M  736M  20% /boot
/dev/mapper/fedora-home  240G   16G  212G   8% /home
tmpfs                    375M   16K  375M   1% /run/user/1000

I using Fedora Lxde 25