x2sys_merge: 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/x2sys_merge - 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/x2sys_merge - from package: GMT

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

Error in other languages:
x2sys_merge: bevel nie gevind nie
x2sys_merge: comandă negăsită
x2sys_merge: comando não encontrado
x2sys_merge: commande introuvable
x2sys_merge: command not found
x2sys_merge: käsku ei ole
x2sys_merge: không tìm thấy lệnh
x2sys_merge: komanda nerasta
x2sys_merge: Kommando nicht gefunden.
x2sys_merge: kommandot finns inte
x2sys_merge: komut yok
x2sys_merge: nie znaleziono polecenia
x2sys_merge: níor aimsíodh an t-ordú
x2sys_merge: no se encontró la orden
x2sys_merge: no s'ha trobat l'ordre
x2sys_merge: opdracht niet gevonden
x2sys_merge: parancs nem található
x2sys_merge: perintah tidak ditemukan
x2sys_merge: príkaz nenájdený
x2sys_merge: příkaz nenalezen
x2sys_merge: команда не найдена
x2sys_merge: командата не е открита
x2sys_merge: 命令找不到
x2sys_merge: コマンドが見つかりません