gmtselect: 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/gmtselect - 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/gmtselect - from package: GMT

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

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