ib_acme: 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/ib_acme - from package: ibacm

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

On Debian possible default full paths are:

/usr/bin/ib_acme - from package: ibacm

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

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