seahorse: 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/seahorse - from package: seahorse

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

On Debian possible default full paths are:

/usr/bin/seahorse - from package: seahorse

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

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