ubuntu@localhost:~$ ls -l /dev/ptmx
crw-rw-rw- 1 root tty 5, 2 Feb 11 16:28 /dev/ptmx
ubuntu@localhost:~$ mount | grep "on /dev"
udev on /dev type devtmpfs (rw,nosuid,relatime,size=833568k,nr_inodes=208392,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)