ns-slapd: 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/ns-slapd - from package: 389-ds-base

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

On Debian possible default full paths are:

/usr/sbin/ns-slapd - from package: 389-ds-base

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

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