fb_smp_server: 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/fb_smp_server - from package: firebird-superclassic

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

On Debian possible default full paths are:

/usr/sbin/fb_smp_server - from package: firebird2.5-superclassic

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

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