fence_imm: 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/fence_imm - from package: fence-agents

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

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