concavity: 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/concavity - from package: concavity

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

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