chef-client: 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 Debian possible default full paths are:

/usr/bin/chef-client - from package: chef

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

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