dolphin: 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/dolphin - from package: kdebase

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

On Debian possible default full paths are:

/usr/bin/dolphin - from package: dolphin

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

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