blockmean: 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/blockmean - 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/blockmean - from package: GMT

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

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