classad_version: 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/classad_version - from package: classads-devel
/usr/bin/classad_version - from package: condor-classads-devel

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

On Debian possible default full paths are:

/usr/bin/classad_version - from package: htcondor

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

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