xournal: 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/xournal - from package: xournal

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

On Debian possible default full paths are:

/usr/bin/xournal - from package: xournal

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

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