ldm-dialog: 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/bin/ldm-dialog - from package: ldm

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

On Debian possible default full paths are:

/usr/bin/ldm-dialog - from package: ldm

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

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