ds_unregister: command not found

Have You tried accessing the binary with the full path?

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/ds_unregister - from package: 389-admin

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

On Debian possible default full paths are:

/usr/sbin/ds_unregister - from package: 389-admin

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