$ cat /etc/shells /bin/sh /bin/bash /sbin/nologin /bin/dash /bin/tcsh /bin/csh
$ ll | grep bash -rwxr-xr-x. 1 root root 941880 5月 11 2016 bash lrwxrwxrwx. 1 root root 4 5月 27 2017 sh -> bash
echo $SHELL /bin/bash