lsh-upgrade-key: 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/lsh-upgrade-key - from package: lsh-utils

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

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