.ssh.hmac: command not found

Have You tried accessing the binary with the full path?

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/.ssh.hmac - from package: openssh-clients

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