Linux
幫助！我的伺服器記憶體不足並鎖定，需要硬重啟
我有一個 VPS（記憶體為 256MB），今天掛了不止一次。它完全凍結了，無法通過 SSH 訪問。我必須執行提供商的“強制關機”程序才能將其恢復。然後伺服器持續了幾個小時，然後再做一次。
第一次出現關於記憶體不足並試圖殺死 mysqld 程序的消息。接下來我設法在 syslog 文件中找到了這個：
Sep 23 01:47:34: [16942.757665] [out_of_memory+0x19e/0x1e0] out_of_memory+0x19e/0x1e0 Sep 23 01:47:34: [16942.758875] Out of memory: kill process 5983 (apache2) score 57519 or a child我已經將 Apache 和 MySQL 配置為相當注意低 RAM，至少據我所知，我想知道為什麼會發生這種情況。我只是需要升級，還是有什麼問題？
這是我的 Apache 配置的摘錄：
# # Timeout: The number of seconds before receives and sends time out. # Timeout 30 # # KeepAlive: Whether or not to allow persistent connections (more than # one request per connection). Set to "Off" to deactivate. # KeepAlive On # # MaxKeepAliveRequests: The maximum number of requests to allow # during a persistent connection. Set to 0 to allow an unlimited amount. # We recommend you leave this number high, for maximum performance. # MaxKeepAliveRequests 200 # # KeepAliveTimeout: Number of seconds to wait for the next request from the # same client on the same connection. # KeepAliveTimeout 3 ## ## Server-Pool Size Regulation (MPM specific) ## # prefork MPM # StartServers: number of server processes to start # MinSpareServers: minimum number of server processes which are kept spare # MaxSpareServers: maximum number of server processes which are kept spare # MaxClients: maximum number of server processes allowed to start # MaxRequestsPerChild: maximum number of requests a server process serves <IfModule mpm_prefork_module> StartServers 1 MinSpareServers 1 MaxSpareServers 3 MaxClients 50 MaxRequestsPerChild 1000 </IfModule>還有我的 MySQL 配置：
[mysqld] # # * Basic Settings # # # * IMPORTANT # If you make changes to these settings and your system uses apparmor, you may # also need to also adjust /etc/apparmor.d/usr.sbin.mysqld. # user = mysql pid-file = /var/run/mysqld/mysqld.pid socket = /var/run/mysqld/mysqld.sock port = 3306 basedir = /usr datadir = /var/lib/mysql tmpdir = /tmp language = /usr/share/mysql/english skip-external-locking skip-locking # # Instead of skip-networking the default is now to listen only on # localhost which is more compatible and is not less secure. bind-address = 127.0.0.1 # # * Fine Tuning # key_buffer = 16K max_allowed_packet = 1M thread_stack = 64K thread_cache_size = 4 sort_buffer = 64K net_buffer_length = 2K #max_connections = 100 #table_cache = 64 #thread_concurrency = 10 # # * Query Cache Configuration # query_cache_limit = 500k #was 1M query_cache_size = 8M #was 16M, lowered for RAM # # * Logging and Replication # # Both location gets rotated by the cronjob. # Be aware that this log type is a performance killer. #log = /var/log/mysql/mysql.log # # Error logging goes to syslog. This is a Debian improvement :) # # Here you can see queries with especially long duration #log_slow_queries = /var/log/mysql/mysql-slow.log #long_query_time = 2 #log-queries-not-using-indexes # # The following can be used as easy to replay backup logs or for replication. # note: if you are setting up a replication slave, see README.Debian about # other settings you may need to change. #server-id = 1 #log_bin = /var/log/mysql/mysql-bin.log expire_logs_days = 10 max_binlog_size = 100M #binlog_do_db = include_database_name #binlog_ignore_db = include_database_name # # * BerkeleyDB # # Using BerkeleyDB is now discouraged as its support will cease in 5.1.12. skip-bdb # # * InnoDB # # InnoDB is enabled by default with a 10MB datafile in /var/lib/mysql/. # Read the manual for more InnoDB related options. There are many! # You might want to disable InnoDB to shrink the mysqld process by circa 100MB. skip-innodb # # * Security Features # # Read the manual, too, if you want chroot! # chroot = /var/lib/mysql/ # # For generating SSL certificates I recommend the OpenSSL GUI "tinyca". # # ssl-ca=/etc/mysql/cacert.pem # ssl-cert=/etc/mysql/server-cert.pem # ssl-key=/etc/mysql/server-key.pem [mysqldump] quick quote-names max_allowed_packet = 16M [mysql] #no-auto-rehash # faster start of mysql but no tab completition [isamchk] key_buffer = 16M如果它有幫助，這裡
ps aux是重啟後大約 20-30 分鐘的輸出：USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.3 3992 920 ? Ss 01:53 0:00 /sbin/init root 2 0.0 0.0 0 0 ? S< 01:53 0:00 [kthreadd] root 3 0.0 0.0 0 0 ? S< 01:53 0:00 [migration/0] root 4 0.0 0.0 0 0 ? S< 01:53 0:00 [ksoftirqd/0] root 5 0.0 0.0 0 0 ? S< 01:53 0:00 [watchdog/0] root 6 0.0 0.0 0 0 ? S< 01:53 0:00 [events/0] root 7 0.0 0.0 0 0 ? S< 01:53 0:00 [khelper] root 18 0.0 0.0 0 0 ? S< 01:53 0:00 [xenwatch] root 19 0.0 0.0 0 0 ? S< 01:53 0:00 [xenbus] root 27 0.0 0.0 0 0 ? S< 01:53 0:00 [migration/1] root 28 0.0 0.0 0 0 ? S< 01:53 0:00 [ksoftirqd/1] root 29 0.0 0.0 0 0 ? S< 01:53 0:00 [watchdog/1] root 30 0.0 0.0 0 0 ? S< 01:53 0:00 [events/1] root 54 0.0 0.0 0 0 ? S< 01:53 0:00 [kblockd/0] root 55 0.0 0.0 0 0 ? S< 01:53 0:00 [kblockd/1] root 65 0.0 0.0 0 0 ? S< 01:53 0:00 [kseriod] root 104 0.0 0.0 0 0 ? S 01:53 0:00 [pdflush] root 105 0.0 0.0 0 0 ? S 01:53 0:00 [pdflush] root 106 0.0 0.0 0 0 ? S< 01:53 0:00 [kswapd0] root 107 0.0 0.0 0 0 ? S< 01:53 0:00 [aio/0] root 108 0.0 0.0 0 0 ? S< 01:53 0:00 [aio/1] root 124 0.0 0.0 0 0 ? S< 01:53 0:00 [accel_watch/0] root 125 0.0 0.0 0 0 ? S< 01:53 0:00 [accel_watch/1] root 2031 0.0 0.0 0 0 ? S< 01:53 0:00 [kjournald] root 2192 0.0 0.3 16848 944 ? S<s 01:53 0:00 /sbin/udevd --daemon syslog 3514 0.0 0.2 12296 728 ? Ss 01:53 0:00 /sbin/syslogd -u syslog root 3534 0.0 0.2 8132 592 ? S 01:53 0:00 /bin/dd bs 1 if /proc/kmsg of /var/run/klogd/kmsg klog 3537 0.0 0.8 5600 2292 ? Ss 01:53 0:00 /sbin/klogd -P /var/run/klogd/kmsg root 3556 0.0 0.4 50916 1160 ? Ss 01:53 0:00 /usr/sbin/sshd root 3776 0.0 0.8 36684 2152 ? Ss 01:53 0:00 /usr/lib/postfix/master postfix 3794 0.0 0.8 38740 2140 ? S 01:53 0:00 pickup -l -t fifo -u -c postfix 3795 0.0 0.8 38784 2228 ? S 01:53 0:00 qmgr -l -t fifo -u root 3802 0.0 0.2 12460 644 ? Ss 01:53 0:00 /usr/sbin/dovecot root 3815 0.0 1.0 71648 2876 ? S 01:53 0:00 dovecot-auth daemon 3816 0.0 0.1 16428 428 ? Ss 01:53 0:00 /usr/sbin/atd root 3829 0.0 0.3 18616 976 ? Ss 01:53 0:00 /usr/sbin/cron dovecot 3851 0.0 0.7 14148 1876 ? S 01:53 0:00 imap-login dovecot 3852 0.0 0.7 14148 1876 ? S 01:53 0:00 imap-login dovecot 3853 0.0 0.7 14148 1876 ? S 01:53 0:00 imap-login root 3875 0.0 0.2 3864 592 tty1 Ss+ 01:53 0:00 /sbin/getty 38400 tty1 root 3913 0.0 1.1 68272 3116 ? Ss 01:54 0:00 sshd: root@pts/0 postfix 3917 0.0 1.1 41248 2964 ? S 01:54 0:00 tlsmgr -l -t unix -u -c root 3924 0.0 0.7 18908 2080 pts/0 Ss 01:54 0:00 -bash root 3958 0.0 0.2 3864 592 ? Ss 01:55 0:00 /sbin/getty 38400 console root 4232 0.0 0.2 3944 608 pts/0 S 02:22 0:00 /bin/sh /usr/bin/mysqld_safe mysql 4271 0.1 5.0 124404 13244 pts/0 Sl 02:22 0:02 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --user=mysql --pi root 4272 0.0 0.2 5068 768 pts/0 S 02:22 0:00 logger -p daemon.err -t mysqld_safe -i -t mysqld root 4415 0.0 3.6 201880 9516 ? Ss 02:29 0:00 /usr/sbin/apache2 -k start www-data 4527 0.5 11.9 225720 31340 ? S 02:47 0:01 /usr/sbin/apache2 -k start www-data 4539 0.6 12.2 226492 32092 ? S 02:50 0:00 /usr/sbin/apache2 -k start www-data 4541 2.3 12.1 226492 31992 ? S 02:52 0:00 /usr/sbin/apache2 -k start root 4544 0.0 0.4 15064 1088 pts/0 R+ 02:53 0:00 ps aux有人可以幫我從這裡出去嗎？
你真的需要修剪你的服務。更好的是，您可能需要考慮使用 inetd 或 xinetd（無論哪個適用於您的安裝）。與其讓多個服務啟動並等待（並佔用寶貴的 RAM），不如在需要時啟動服務來降低 CPU 性能。這就是 inetd/xinetd 的真正意義——它們旨在提供一種低記憶體方式來允許服務按需啟動，而不是讓它們一直閒逛。當然，你的里程可能非常 - 你仍然可能會遇到記憶體資源問題 - 但如果它讓你暫時度過難關……
跟進從哪裡開始（來自評論）：
我會先考慮讓 apache 移過來。將最大子數減少到只有 2 個 - 除非您為比自己更多的使用者提供服務，否則擁有 3 個正在執行的程序幾乎沒有幫助。
對於 dovecot，特別是 imap-auth 程序，您只需要一個。您也可以在 inetd 中執行它，儘管它看起來相當薄。如果您不在伺服器上使用 IMAP 或 POP，請將其關閉。最壞的情況是，您又回到了在命令行中閱讀郵件的狀態——雖然不是很漂亮但很實用。
您也可以移動 sshd，儘管我最初會在另一個埠號上執行此操作，並在您打開該埠號之前確認它已連接。
如果可能，考慮遷移到 Exim（這是 Debian/Ubuntu 設置的預設安裝）。我喜歡 Postfix，而且我不使用 Exim，但 Debian 選擇它作為預設設置是有原因的——它需要的資源很少，而且相當安全。
查看您的 /proc/sys/vm/swappiness 設置 (
echo /proc/sys/vm/swappiness) 並確定它是太高還是太低。更高的數字將有助於釋放記憶體（通過提前交換到 VM），但是當它太高時，你會像瘋了一樣交換。大多數安裝說“60”，但對於低記憶體，它可能應該更像 85。我不建議在您的設置中使用 100。最後，想想“綠屏”。您正在談論在更舊的系統上使用已經存在很長時間的技術（因為它們也受到資源限制）。以這種方式做事有點過時了，但是如果您可以在 shell 中的客戶端程序中完成您的工作，而不是啟動服務，那麼您將進一步擴展您的計算資源。