grdhisteq: 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/grdhisteq - 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/grdhisteq - from package: GMT

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

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