[Dovecot] SYN flooding / pipe() failed: Too many open files

[Frank Elsner]

Hello *,
         I've the following problem with dovecot 1.0.7:


/var/log/messages shows

| Dec 13 13:48:27 mailbox kernel: possible SYN flooding on port 143. Sending cookies.


and /var/log/maillog shows (Please note: nearly the same time):

| Dec 13 13:48:28 mailbox dovecot: pipe() failed: Too many open files


This leads to an unresponsive mail service and requires a dovecot restart.
What can be done to prevent this?


BTW, this is my dovecot -n:

# 1.0.7: /usr/local/dovecot/etc/dovecot.conf
base_dir: /var/run/dovecot/
protocols: imap imaps pop3 pop3s
ssl_cert_file: /usr/local/dovecot/etc/mailbox.pem
ssl_key_file: /usr/local/dovecot/etc/mailbox.key
disable_plaintext_auth: no
login_dir: /var/run/dovecot//login
login_executable(default): /usr/local/dovecot/libexec/dovecot/imap-login
login_executable(imap): /usr/local/dovecot/libexec/dovecot/imap-login
login_executable(pop3): /usr/local/dovecot/libexec/dovecot/pop3-login
login_greeting: TU-Berlin.DE POP3-/IMAP Service ready
login_log_format_elements: %u %r %c
login_processes_count: 24
login_max_processes_count: 512
verbose_proctitle: yes
mail_location: maildir:/var/Mail/Boxes/%1u/%u
mailbox_idle_check_interval: 15
maildir_copy_with_hardlinks: yes
maildir_copy_preserve_filename: yes
mail_executable(default): /usr/local/dovecot/libexec/dovecot/imap
mail_executable(imap): /usr/local/dovecot/libexec/dovecot/imap
mail_executable(pop3): /usr/local/dovecot/libexec/dovecot/pop3
mail_plugins(default): quota imap_quota
mail_plugins(imap): quota imap_quota
mail_plugins(pop3): quota
mail_plugin_dir(default): /usr/local/dovecot/lib/dovecot/imap
mail_plugin_dir(imap): /usr/local/dovecot/lib/dovecot/imap
mail_plugin_dir(pop3): /usr/local/dovecot/lib/dovecot/pop3
mail_log_prefix: %Ls(%u): 
imap_client_workarounds(default): delay-newmail outlook-idle netscape-eoh tb-extra-mailbox-sep
imap_client_workarounds(imap): delay-newmail outlook-idle netscape-eoh tb-extra-mailbox-sep
imap_client_workarounds(pop3): outlook-idle
pop3_uidl_format(default): 
pop3_uidl_format(imap): 
pop3_uidl_format(pop3): %08Xu%08Xv
pop3_client_workarounds(default): 
pop3_client_workarounds(imap): 
pop3_client_workarounds(pop3): outlook-no-nuls oe-ns-eoh
auth default:
  mechanisms: plain login anonymous
  count: 32
  passdb:
    driver: ldap
    args: /usr/local/dovecot/etc/dovecot-ldap.conf
  userdb:
    driver: static
    args: uid=777 gid=12
plugin:
  quota: maildir:ignore=Trash



Kind regards   ______________________________________________________________ 
Frank Elsner  /                        c/o  Technische Universitaet Berlin   |
 ____________/                              tubIT [BD], Sekr. E-N 50         |
|                                           Einsteinufer 17                  |
| Phone: +49 30 314 23897                   D-10587 Berlin                   |
| eMail: Frank.Elsner at TU-Berlin.DE          Germany        __________________|
|_________________________________________________________| in dubio pro exim