sigviewer: 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/sigviewer - from package: sigviewer

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

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