ristosds: 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/ristosds - from package: hdf

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/ristosds - from package: hdf4-tools

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

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