cjrndper: 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/lib/x86_64-linux-gnu/gap/pkg/guava/bin/leon/cjrndper - from package: gap-guava-bin

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

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