mksh: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/bin/mksh - from package: mksh

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/bin/mksh - from package: mksh

You may install the required package with command apt-get install {package}

Error in other languages:
mksh: bevel nie gevind nie
mksh: comandă negăsită
mksh: comando não encontrado
mksh: commande introuvable
mksh: command not found
mksh: käsku ei ole
mksh: không tìm thấy lệnh
mksh: komanda nerasta
mksh: Kommando nicht gefunden.
mksh: kommandot finns inte
mksh: komut yok
mksh: nie znaleziono polecenia
mksh: níor aimsíodh an t-ordú
mksh: no se encontró la orden
mksh: no s'ha trobat l'ordre
mksh: opdracht niet gevonden
mksh: parancs nem található
mksh: perintah tidak ditemukan
mksh: príkaz nenájdený
mksh: příkaz nenalezen
mksh: команда не найдена
mksh: командата не е открита
mksh: 命令找不到
mksh: コマンドが見つかりません