pm-hibernate: 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/sbin/pm-hibernate - from package: pm-utils

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

On Debian possible default full paths are:

/usr/sbin/pm-hibernate - from package: pm-utils

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

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