sea: 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/sea - from package: alliance

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

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