не работает preexec в самбе из lenny

["Andrey N. Prokofiev" <andy@eth0.spb.ru>]

Конфиг самбы:
[global]
       log file = /var/log/samba/log.%m
       socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192
       null passwords = yes
       encrypt passwords = yes
       hosts allow = 192.168.0. 127.
       interfaces = 192.168.0.10/24
       winbind use default domain = yes
       winbind uid = 10000-20000
       case sensitive = no
       dns proxy = no
       netbios name = beta
       server string = beta server
       password server = pdc
       dos charset = 866
       winbind gid = 10000-20000
       local master = no
       workgroup = AUTO
       security = domain
       unix charset = UTF-8
       max log size = 50
       auth methods = winbind
[homes]
       comment = Домашняя директория для %u
       browseable = no
       writable = yes
       create mask = 0640
       directory mask = 0750
       read only = no
       force create mode = 0004
       force directory mode = 0005
       valid users = %u
       preexec =  if [ ! -x /home/samba_shares/%U ]; then mkdir 
/home/samba_shares/%U ; fi

preexec не отрабатывает. в чем может быть причина?