x_over: 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/x_over - from package: GMT

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

On Debian possible default full paths are:

/usr/lib/gmt/bin/x_over - from package: GMT

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

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