gsnap: 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

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/gsnap - from package: snap-gtk

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