psi-plus: 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/psi-plus - from package: psi-plus

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

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