gnucash: 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/gnucash - from package: gnucash

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

On Debian possible default full paths are:

/usr/bin/gnucash - from package: gnucash

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

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