seqdiag: 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/seqdiag - from package: python-seqdiag

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

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