/ dev / sda1 is a file, not a folder of course, can not cd
you can use ll / dev / sda1 to view its properties
/ Var is full, if not wrong, then
Use the command du -sh *
1. delete the files in the e-mail notification maildrop directory
命令：find /var/spool/postfix/maildrop/ -type f |xargs rm -rf