plymouthd: 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:

/sbin/plymouthd - from package: plymouth

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

On Debian possible default full paths are:

/sbin/plymouthd - from package: plymouth

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

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