Почему вылетает squid?

ОС - Ubuntu Server 16.04 на VPS
uname -a

Linux andrewg 2.6.32-042stab108.5 #1 SMP Wed Jun 17 20:20:17 MSK 2015 x86_64 x86_64 x86_64 GNU/Linux

Конфиг-файл (grep -v "^$\|^#" /etc/squid/squid.conf)

auth_param basic realm ***?
auth_param basic program /etc/webmin/squid/squid-auth.pl /etc/webmin/squid/users
acl Auth proxy_auth REQUIRED
http_access allow Auth
http_access deny all
http_port ****
tcp_outgoing_address ***.***.***.***
cache_dir ufs /var/spool/squid3 256 16 256
cache_log /var/log/squid/squid.log
coredump_dir /var/spool/squid3
pinger_enable off
refresh_pattern ^ftp:           1440    20%     10080
refresh_pattern ^gopher:        1440    0%      1440
refresh_pattern -i (/cgi-bin/|\?) 0     0%      0
refresh_pattern (Release|Packages(.gz)*)$      0       20%     2880
refresh_pattern .               0       20%     4320
cache_effective_user proxy
dns_v4_first on
cache_effective_group proxy
via off
forwarded_for delete

В качестве программы авторизации используется то, что предоставляет webmin.

squid -v

Squid Cache: Version 3.5.12
Service Name: squid
Ubuntu linux
configure options:  '--build=x86_64-linux-gnu' '--prefix=/usr' '--includedir=${prefix}/include' '--mandir=${prefix}/share/man' '--infodir=${prefix}/share/info' '--sysconfdir=/etc' '--localstatedir=/var' '--libexecdir=${prefix}/lib/squid3' '--srcdir=.' '--disable-maintainer-mode' '--disable-dependency-tracking' '--disable-silent-rules' 'BUILDCXXFLAGS=-g -O2 -fPIE -fstack-protector-strong -Wformat -Werror=format-security -Wl,-Bsymbolic-functions -fPIE -pie -Wl,-z,relro -Wl,-z,now' '--datadir=/usr/share/squid' '--sysconfdir=/etc/squid' '--libexecdir=/usr/lib/squid' '--mandir=/usr/share/man' '--enable-inline' '--disable-arch-native' '--enable-async-io=8' '--enable-storeio=ufs,aufs,diskd,rock' '--enable-removal-policies=lru,heap' '--enable-delay-pools' '--enable-cache-digests' '--enable-icap-client' '--enable-follow-x-forwarded-for' '--enable-auth-basic=DB,fake,getpwnam,LDAP,NCSA,NIS,PAM,POP3,RADIUS,SASL,SMB' '--enable-auth-digest=file,LDAP' '--enable-auth-negotiate=kerberos,wrapper' '--enable-auth-ntlm=fake,smb_lm' '--enable-external-acl-helpers=file_userip,kerberos_ldap_group,LDAP_group,session,SQL_session,unix_group,wbinfo_group' '--enable-url-rewrite-helpers=fake' '--enable-eui' '--enable-esi' '--enable-icmp' '--enable-zph-qos' '--enable-ecap' '--disable-translation' '--with-swapdir=/var/spool/squid' '--with-logdir=/var/log/squid' '--with-pidfile=/var/run/squid.pid' '--with-filedescriptors=65536' '--with-large-files' '--with-default-user=proxy' '--enable-build-info=Ubuntu linux' '--enable-linux-netfilter' 'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -fPIE -fstack-protector-strong -Wformat -Werror=format-security -Wall' 'LDFLAGS=-Wl,-Bsymbolic-functions -fPIE -pie -Wl,-z,relro -Wl,-z,now' 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2' 'CXXFLAGS=-g -O2 -fPIE -fstack-protector-strong -Wformat -Werror=format-security'

Вот логи
cat /var/log/syslog | grep squid

Aug  5 12:19:34 andrew squid[20873]: Squid Parent: (squid-1) process 20875 started
Aug  5 22:24:48 andrew squid[20873]: Squid Parent: (squid-1) process 20875 exited due to signal 9 with status 0

cat /var/log/squid/squid.log (этот файл я указал в переменной cache_log)

2016/08/05 12:19:34 kid1| Set Current Directory to /var/spool/squid3
2016/08/05 12:19:34 kid1| Starting Squid Cache version 3.5.12 for x86_64-pc-linux-gnu...
2016/08/05 12:19:34 kid1| Service Name: squid
2016/08/05 12:19:34 kid1| Process ID 20875
2016/08/05 12:19:34 kid1| Process Roles: worker
2016/08/05 12:19:34 kid1| With 65535 file descriptors available
2016/08/05 12:19:34 kid1| Initializing IP Cache...
2016/08/05 12:19:34 kid1| DNS Socket created at [::], FD 6
2016/08/05 12:19:34 kid1| DNS Socket created at 0.0.0.0, FD 8
2016/08/05 12:19:34 kid1| Adding nameserver 8.8.8.8 from /etc/resolv.conf
2016/08/05 12:19:34 kid1| Adding nameserver 8.8.4.4 from /etc/resolv.conf
2016/08/05 12:19:34 kid1| helperOpenServers: Starting 0/20 'squid-auth.pl' processes
2016/08/05 12:19:34 kid1| helperOpenServers: No 'squid-auth.pl' processes needed.
2016/08/05 12:19:34 kid1| Logfile: opening log daemon:/var/log/squid/access.log
2016/08/05 12:19:34 kid1| Logfile Daemon: opening log /var/log/squid/access.log
2016/08/05 12:19:34 kid1| Unlinkd pipe opened on FD 14
2016/08/05 12:19:34 kid1| Local cache digest enabled; rebuild/rewrite every 3600/3600 sec
2016/08/05 12:19:34 kid1| Store logging disabled
2016/08/05 12:19:34 kid1| Swap maxSize 262144 + 262144 KB, estimated 40329 objects
2016/08/05 12:19:34 kid1| Target number of buckets: 2016
2016/08/05 12:19:34 kid1| Using 8192 Store buckets
2016/08/05 12:19:34 kid1| Max Mem  size: 262144 KB
2016/08/05 12:19:34 kid1| Max Swap size: 262144 KB
2016/08/05 12:19:35 kid1| Rebuilding storage in /var/spool/squid3 (dirty log)
2016/08/05 12:19:35 kid1| Using Least Load store dir selection
2016/08/05 12:19:35 kid1| Set Current Directory to /var/spool/squid3
2016/08/05 12:19:36 kid1| Finished loading MIME types and icons.
2016/08/05 12:19:36 kid1| HTCP Disabled.
2016/08/05 12:19:36 kid1| Squid plugin modules loaded: 0
2016/08/05 12:19:36 kid1| Adaptation support is off.
2016/08/05 12:19:36 kid1| Accepting HTTP Socket connections at local=[::]:****remote=[::] FD 17 flags=9
2016/08/05 12:19:36 kid1| Store rebuilding is 21.44% complete
2016/08/05 12:19:36 kid1| Done reading /var/spool/squid3 swaplog (18653 entries)
2016/08/05 12:19:36 kid1| Finished rebuilding storage from disk.
2016/08/05 12:19:36 kid1|     12656 Entries scanned
2016/08/05 12:19:36 kid1|         9 Invalid entries.
2016/08/05 12:19:36 kid1|         0 With invalid flags.
2016/08/05 12:19:36 kid1|     11674 Objects loaded.
2016/08/05 12:19:36 kid1|         0 Objects expired.
2016/08/05 12:19:36 kid1|         0 Objects cancelled.
2016/08/05 12:19:36 kid1|       180 Duplicate URLs purged.
2016/08/05 12:19:36 kid1|       802 Swapfile clashes avoided.
2016/08/05 12:19:36 kid1|   Took 1.33 seconds (8777.01 objects/sec).
2016/08/05 12:19:36 kid1| Beginning Validation Procedure
2016/08/05 12:19:36 kid1|   Completed Validation Procedure
2016/08/05 12:19:36 kid1|   Validated 11674 Entries
2016/08/05 12:19:36 kid1|   store_swap_size = 385740.00 KB
2016/08/05 12:19:39 kid1| storeLateRelease: released 0 objects
2016/08/05 12:19:54 kid1| Starting new basicauthenticator helpers...
2016/08/05 12:19:54 kid1| helperOpenServers: Starting 1/20 'squid-auth.pl' processes
2016/08/05 12:59:36 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 12:59:36 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 12:59:36 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 13:41:15 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 13:41:15 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 13:41:15 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 14:35:50 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 14:35:50 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 14:35:50 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 15:35:20 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 15:35:20 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 15:35:20 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 16:33:30 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 16:33:30 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 16:33:30 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 17:46:46 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 17:46:46 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 17:46:46 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 18:49:29 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 18:49:29 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 18:49:29 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 19:31:31 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 19:31:31 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 19:31:31 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 20:12:16 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 20:12:16 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 20:12:16 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 21:02:22 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 21:02:22 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 21:02:22 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 22:17:24 kid1| Logfile: opening log stdio:/var/log/squid/netdb.state
2016/08/05 22:17:24 kid1| Logfile: closing log stdio:/var/log/squid/netdb.state
2016/08/05 22:17:24 kid1| NETDB state saved; 0 entries, 0 msec
2016/08/05 22:24:47 kid1| WARNING: basicauthenticator #Hlpr1 exited
2016/08/05 22:24:48 kid1| Too few basicauthenticator processes are running (need 1/20)
2016/08/05 22:24:48 kid1| Starting new helpers
2016/08/05 22:24:48 kid1| helperOpenServers: Starting 1/20 'squid-auth.pl' processes

Squid падает регулярно, каждый день или через день, иногда несколько раз в день.
В чем может быть проблема?