dphys-config-altern-xsession: 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/share/doc/dphys-config/examples/site.example/local/sbin/dphys-config-altern-xsession - from package: dphys-config

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

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