gtroff: 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 CentOS possible default full paths are:

/usr/bin/gtroff - from package: groff

You may install the required package with command yum install {package}

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