gman: 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/gman - from package: gman

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

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