Linux prompt bash:command not found

                  If the newly installed system runs some very normal commands such as shutdown and fdisk, it prompts: bash:command not found. So first consider whether these environment variables are already included in the root $PATH. Mainly these four: /bin, /usr/bin, /sbin, /usr/sbin. The four main deposits: ./bin: bin is a shorthand for binary. It mainly places some necessary executable files for the system: cat, cp, chmod df, dmesg, gzip, kill, ls, mkdir, more, mount, rm , su, tar, etc. /usr/bin: Main executable files for some application software tools such as c++, g++, gcc, chdrv, diff, dig, du, eject, elm, free, gnome*, gzip, htpasswd, kfm, ktop, last, Less, locale, m4, make, man, mcopy, ncftp, newaliases, nslookup passwd, quota, smb*, wget, etc. /sbin: Mainly put some system management necessary programs such as: cfdisk, dhcpcd, dump, e2fsck, fdisk, halt, ifconfig, ifup, ifdown, init, insmod, lilo, lsmod, mke2fs, modprobe, quotacheck, reboot, rmmod, Runlevel, shutdown, etc. /usr/sbin: Place some necessary programs for network management such as: dhcpd, httpd, imap, in.*d, inetd, lpd, named, netconfig, nmbd, samba, sendmail, squid, swap, tcpd, tcpdump, etc. You can view the PATH in .bash_profile in the home directory. If it is: PATH=$PATH:$HOME/bin, you need to add it as follows: PATH=$PATH:$HOME/bin:/sbin:/usr/bin:/usr/sbin