segy2grd: 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/segy2grd - 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/segy2grd - from package: GMT

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

Error in other languages:
segy2grd: bevel nie gevind nie
segy2grd: comandă negăsită
segy2grd: comando não encontrado
segy2grd: commande introuvable
segy2grd: command not found
segy2grd: käsku ei ole
segy2grd: không tìm thấy lệnh
segy2grd: komanda nerasta
segy2grd: Kommando nicht gefunden.
segy2grd: kommandot finns inte
segy2grd: komut yok
segy2grd: nie znaleziono polecenia
segy2grd: níor aimsíodh an t-ordú
segy2grd: no se encontró la orden
segy2grd: no s'ha trobat l'ordre
segy2grd: opdracht niet gevonden
segy2grd: parancs nem található
segy2grd: perintah tidak ditemukan
segy2grd: príkaz nenájdený
segy2grd: příkaz nenalezen
segy2grd: команда не найдена
segy2grd: командата не е открита
segy2grd: 命令找不到
segy2grd: コマンドが見つかりません