lsh-keygen: 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-keygen - from package: lsh-utils

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

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