spacewalk-channel: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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 Debian possible default full paths are:

/usr/sbin/spacewalk-channel - from package: rhn-client-tools

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