system.o: command not found

Have You tried accessing the binary with the full path?

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/bin/system.o - from package: gap-dev

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