visudo: 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:

/usr/sbin/visudo - from package: sudo

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

On Debian possible default full paths are:

/usr/sbin/visudo - from package: sudo-ldap
/usr/sbin/visudo - from package: sudo

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

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