condor_who: 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/condor_who - from package: condor

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

On Debian possible default full paths are:

/usr/bin/condor_who - from package: htcondor

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

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