psmshell: 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
/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/psmshell - from package: ion

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