ldapmodrdn: 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/ldapmodrdn - from package: openldap-clients
/usr/share/doc/perl-LDAP-0.40/bin/ldapmodrdn - from package: perl-LDAP

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

On Debian possible default full paths are:

/usr/bin/ldapmodrdn - from package: ldap-utils

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

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