slapdn: 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/slapdn - from package: openldap-servers

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

On Debian possible default full paths are:

/usr/sbin/slapdn - from package: slapd

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

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