sslh: 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/sslh - from package: sslh

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

On Debian possible default full paths are:

/usr/sbin/sslh - from package: sslh
/usr/bin/sslh - from package: libnet-proxy-perl

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

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