11.7. 設定系統日誌
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## 11.7. 設定系統日誌

Contributed by Niclas Zeising.

產生與讀取系統日誌對系統管理來說是一件非常重要的事，在系統日誌中的資訊可以用來偵測硬體與軟體的問題，同樣也可以偵測應用程式與系統設定的錯誤。這些資訊在安全性稽查與事件回應也同樣扮演了重要的角色，大多數系統 Daemon 與應用程式都會產生日誌項目。

FreeBSD 提供了一個系統日誌程式 syslogd 用來管理日誌。預設 syslogd 會與系統開機時啟動。這可使用在 `/etc/rc.conf` 中的變數 `syslogd_enable` 來控制。而且有數個應用程式參數可在 `/etc/rc.conf` 使用 `syslogd_flags` 來設定。請參考 syslogd(8) 來取得更多可用參數的資訊。

此章節會介紹如何設定 FreeBSD 系統日誌程式來做本地與遠端日誌並且介紹如何執行日誌翻轉 (Log rotation) 與日誌管理。

### 11.7.1. 設定本地日誌

設定檔 `/etc/syslog.conf` 控制 syslogd 收到日誌項目時要做的事情，有數個參數可以用來控制接收到事件時的處理方式。設施 (facility) 用來描述記錄產生訊息的子系統 (subsystem)，如核心或者 Daemon，而 層級 (level) 用來描述所發生的事件嚴重性。也可以依據應用程式所發出的訊息及產生日誌事件機器的主機名稱來決定後續處置的動作。

此設定檔中一行代表一個動作，每一行的格式皆為一個選擇器欄位 (Selector field) 接著一個動作欄位 (Action field)。選擇器欄位的格式為 `facility.level` 可以用來比對來自 `facility` 於層級 `level` 或更高層的日誌訊息，也可以在層級前加入選擇性的比對旗標來更確切的指定記錄的內容。同樣一個動作可以使用多個選擇器欄位並使用分號 (`;`) 來分隔。用 `*` 可以比對任何東西。動作欄位可用來指定傳送日誌訊息的目標，如一個檔案或遠端日誌主機。範例為以下為 FreeBSD 預設的 `syslog.conf`：

    # $FreeBSD: head/zh_TW.UTF-8/books/handbook/book.xml 52701 2018-12-20 06:29:19Z rcyu $
    #
    #       Spaces ARE valid field separators in this file. However,
    #       other *nix-like systems still insist on using tabs as field
    #       separators. If you are sharing this file between systems, you
    #       may want to use only tabs as field separators here.
    #       Consult the syslog.conf(5) manpage.
    *.err;kern.warning;auth.notice;mail.crit                /dev/console
    *.notice;authpriv.none;kern.debug;lpr.info;mail.crit;news.err   /var/log/messages
    security.*                                      /var/log/security
    auth.info;authpriv.info                         /var/log/auth.log
    mail.info                                       /var/log/maillog
    lpr.info                                        /var/log/lpd-errs
    ftp.info                                        /var/log/xferlog
    cron.*                                          /var/log/cron
    !-devd
    *.=debug                                        /var/log/debug.log
    *.emerg                                         *
    # uncomment this to log all writes to /dev/console to /var/log/console.log
    #console.info                                   /var/log/console.log
    # uncomment this to enable logging of all log messages to /var/log/all.log
    # touch /var/log/all.log and chmod it to mode 600 before it will work
    #*.*                                            /var/log/all.log
    # uncomment this to enable logging to a remote loghost named loghost
    #*.*                                            @loghost
    # uncomment these if you're running inn
    # news.crit                                     /var/log/news/news.crit
    # news.err                                      /var/log/news/news.err
    # news.notice                                   /var/log/news/news.notice
    # Uncomment this if you wish to see messages produced by devd
    # !devd
    # *.>=info
    !ppp
    *.*                                             /var/log/ppp.log
    !*

在這個範例中：

- 第 8 行會找出所有符合 `err` 或以上層級的訊息，還有 `kern.warning`, `auth.notice` 與 `mail.crit` 的訊息，然後將這些日誌訊息傳送到 Console (`/dev/console`)。

- 第 12 行會找出所有符合 `mail` 設施中於 `info` 或以上層級的訊息，並記錄訊息至 `/var/log/maillog`。

- 第 17 行使用了比較旗標 (`=`) 來只找出符合 `debug` 層級的訊息，並將訊息記錄至 `/var/log/debug.log`。

- 第 33 行是指定程式的範例用法。這可以讓在該行以下的規則只對指定的程式生效。在此例中，只有由 ppp 產生的訊息會被記錄到 `/var/log/ppp.log`。

所以可用層級從最嚴重到最不嚴重的順序為 `emerg`, `alert`, `crit`, `err`, `warning`, `notice`, `info` 以及 `debug`。

設施 (facility) 則無特定順序，可用的有 `auth`, `authpriv`, `console`, `cron`, `daemon`, `ftp`, `kern`, `lpr`, `mail`, `mark`, `news`, `security`, `syslog`, `user`, `uucp` 及 `local0` 到 `local7`。要注意在其他作業系統的設施可能會不同。

要記錄所有所有 `notice` 與以上層級的訊息到 `/var/log/daemon.log` 可加入以下項目：

    daemon.notice                                        /var/log/daemon.log

要取得更多有關不同的層級與設施的資訊請參考 syslog(3) 及 syslogd(8)。要取得更多有關 `/etc/syslog.conf`、語法以及更多進階用法範例的資訊請參考 syslog.conf(5)。

### 11.7.2. 日誌管理與翻轉

日誌檔案會成長的非常快速，這會消耗磁碟空間並且會更難在日誌中找到有用的資訊，日誌管理便是為了嘗試減緩這種問題。在 FreeBSD 可以使用 newsyslog 來管理日誌檔案，這個內建的程式會定期翻轉 (Rotate) 與壓縮日誌檔案，並且可選擇性的建立遺失的日誌檔案並在日誌檔案被移動位置時通知程式。日誌檔案可能會由 syslogd 產生或由其他任何會產生日誌檔案的程式。newsyslog 正常會由 cron(8) 來執行，它並非一個系統 Daemon，預設會每個小時執行一次。

newsyslog 會讀取其設定檔 `/etc/newsyslog.conf` 來決定其要採取的動作，每個要由 newsyslog 所管理的日誌檔案會在此設定檔中設定一行，每一行要說明檔案的擁有者、權限、何時要翻轉該檔案、選用的日誌翻轉旗標，如：壓縮，以及日誌翻轉時要通知的程式。以下為 FreeBSD 的預設設定：

    # configuration file for newsyslog
    # $FreeBSD: head/zh_TW.UTF-8/books/handbook/book.xml 52701 2018-12-20 06:29:19Z rcyu $
    #
    # Entries which do not specify the '/pid_file' field will cause the
    # syslogd process to be signalled when that log file is rotated.  This
    # action is only appropriate for log files which are written to by the
    # syslogd process (ie, files listed in /etc/syslog.conf).  If there
    # is no process which needs to be signalled when a given log file is
    # rotated, then the entry for that file should include the 'N' flag.
    #
    # The 'flags' field is one or more of the letters: BCDGJNUXZ or a '-'.
    #
    # Note: some sites will want to select more restrictive protections than the
    # defaults.  In particular, it may be desirable to switch many of the 644
    # entries to 640 or 600.  For example, some sites will consider the
    # contents of maillog, messages, and lpd-errs to be confidential.  In the
    # future, these defaults may change to more conservative ones.
    #
    # logfilename          [owner:group]    mode count size when  flags [/pid_file] [sig_num]
    /var/log/all.log                        600  7     *    @T00  J
    /var/log/amd.log                        644  7     100  *     J
    /var/log/auth.log                       600  7     100  @0101T JC
    /var/log/console.log                    600  5     100  *     J
    /var/log/cron                           600  3     100  *     JC
    /var/log/daily.log                      640  7     *    @T00  JN
    /var/log/debug.log                      600  7     100  *     JC
    /var/log/kerberos.log                   600  7     100  *     J
    /var/log/lpd-errs                       644  7     100  *     JC
    /var/log/maillog                        640  7     *    @T00  JC
    /var/log/messages                       644  5     100  @0101T JC
    /var/log/monthly.log                    640  12    *    $M1D0 JN
    /var/log/pflog                          600  3     100  *     JB    /var/run/pflogd.pid
    /var/log/ppp.log        root:network    640  3     100  *     JC
    /var/log/devd.log                       644  3     100  *     JC
    /var/log/security                       600  10    100  *     JC
    /var/log/sendmail.st                    640  10    *    168   B
    /var/log/utx.log                        644  3     *    @01T05 B
    /var/log/weekly.log                     640  5     1    $W6D0 JN
    /var/log/xferlog                        600  7     100  *     JC

每一行的開始為要翻轉的日誌名稱、接著是供翻轉與新建檔案使用的擁有者及群組 (選填)。`mode` 欄位可設定日誌檔案的權限，`count` 代表要保留多少個翻轉過的日誌檔案，而 `size` 與 `when` 欄位會告訴 newsyslog 何時要翻轉該檔案。日誌檔案會在當其檔案超過 `size` 欄位的大小或已超過 `when` 欄位指定的時間時翻轉，可使用星號 (`*`) 忽略該欄位。`flags` 欄位可以給予進階的參數，例如：如何壓縮翻轉後檔案或建立遺失的日誌檔案。最後兩個欄位皆為選填，可指定程序的程序 ID (PID) 檔名稱以及檔案翻轉後要傳送給該程序的信號 (Signal) 編號。

要取的更多有關所有欄位、可用的旗標及如何指定翻轉時間，請參考 newsyslog.conf(5)。由於 newsyslog 是由 cron(8) 執行，因此無法比其在 cron(8) 中所排定的時間間距內更頻繁的執行翻轉檔案。

### 11.7.3. 設定遠端日誌

Contributed by Tom Rhodes.

Monitoring the log files of multiple hosts can become unwieldy as the number of systems increases. Configuring centralized logging can reduce some of the administrative burden of log file administration.

In FreeBSD, centralized log file aggregation, merging, and rotation can be configured using syslogd and newsyslog. This section demonstrates an example configuration, where host `A`, named `logserv.example.com`, will collect logging information for the local network. Host `B`, named `logclient.example.com`, will be configured to pass logging information to the logging server.

#### 11.7.3.1. 日誌伺服器設定

A log server is a system that has been configured to accept logging information from other hosts. Before configuring a log server, check the following:

- If there is a firewall between the logging server and any logging clients, ensure that the firewall ruleset allows UDP port 514 for both the clients and the server.

- The logging server and all client machines must have forward and reverse entries in the local DNS. If the network does not have a DNS server, create entries in each system's `/etc/hosts`. Proper name resolution is required so that log entries are not rejected by the logging server.

On the log server, edit `/etc/syslog.conf` to specify the name of the client to receive log entries from, the logging facility to be used, and the name of the log to store the host's log entries. This example adds the hostname of `B`, logs all facilities, and stores the log entries in `/var/log/logclient.log`.

範例 11.1. 日誌伺服器設定範例

    +logclient.example.com
    *.*     /var/log/logclient.log

When adding multiple log clients, add a similar two-line entry for each client. More information about the available facilities may be found in syslog.conf(5).

Next, configure `/etc/rc.conf`:

    syslogd_enable="YES"
    syslogd_flags="-a logclient.example.com -v -v"

The first entry starts syslogd at system boot. The second entry allows log entries from the specified client. The `-v -v` increases the verbosity of logged messages. This is useful for tweaking facilities as administrators are able to see what type of messages are being logged under each facility.

Multiple `-a` options may be specified to allow logging from multiple clients. IP addresses and whole netblocks may also be specified. Refer to syslogd(8) for a full list of possible options.

Finally, create the log file:

    # touch /var/log/logclient.log

At this point, syslogd should be restarted and verified:

    # service syslogd restart
    # pgrep syslog

If a PID is returned, the server restarted successfully, and client configuration can begin. If the server did not restart, consult `/var/log/messages` for the error.

#### 11.7.3.2. 日誌客戶端設定

A logging client sends log entries to a logging server on the network. The client also keeps a local copy of its own logs.

Once a logging server has been configured, edit `/etc/rc.conf` on the logging client:

    syslogd_enable="YES"
    syslogd_flags="-s -v -v"

The first entry enables syslogd on boot up. The second entry prevents logs from being accepted by this client from other hosts (`-s`) and increases the verbosity of logged messages.

Next, define the logging server in the client's `/etc/syslog.conf`. In this example, all logged facilities are sent to a remote system, denoted by the `@` symbol, with the specified hostname:

    *.*		@logserv.example.com

After saving the edit, restart syslogd for the changes to take effect:

    # service syslogd restart

To test that log messages are being sent across the network, use logger(1) on the client to send a message to syslogd:

    # logger "Test message from logclient"

This message should now exist both in `/var/log/messages` on the client and `/var/log/logclient.log` on the log server.

#### 11.7.3.3. 日誌伺服器除錯

If no messages are being received on the log server, the cause is most likely a network connectivity issue, a hostname resolution issue, or a typo in a configuration file. To isolate the cause, ensure that both the logging server and the logging client are able to `ping` each other using the hostname specified in their `/etc/rc.conf`. If this fails, check the network cabling, the firewall ruleset, and the hostname entries in the DNS server or `/etc/hosts` on both the logging server and clients. Repeat until the `ping` is successful from both hosts.

If the `ping` succeeds on both hosts but log messages are still not being received, temporarily increase logging verbosity to narrow down the configuration issue. In the following example, `/var/log/logclient.log` on the logging server is empty and `/var/log/messages` on the logging client does not indicate a reason for the failure. To increase debugging output, edit the `syslogd_flags` entry on the logging server and issue a restart:

    syslogd_flags="-d -a logclient.example.com -v -v"

    # service syslogd restart

Debugging data similar to the following will flash on the console immediately after the restart:

    logmsg: pri 56, flags 4, from logserv.example.com, msg syslogd: restart
    syslogd: restarted
    logmsg: pri 6, flags 4, from logserv.example.com, msg syslogd: kernel boot file is /boot/kernel/kernel
    Logging to FILE /var/log/messages
    syslogd: kernel boot file is /boot/kernel/kernel
    cvthname(192.168.1.10)
    validate: dgram from IP 192.168.1.10, port 514, name logclient.example.com;
    rejected in rule 0 due to name mismatch.

In this example, the log messages are being rejected due to a typo which results in a hostname mismatch. The client's hostname should be `logclient`, not `logclien`. Fix the typo, issue a restart, and verify the results:

    # service syslogd restart
    logmsg: pri 56, flags 4, from logserv.example.com, msg syslogd: restart
    syslogd: restarted
    logmsg: pri 6, flags 4, from logserv.example.com, msg syslogd: kernel boot file is /boot/kernel/kernel
    syslogd: kernel boot file is /boot/kernel/kernel
    logmsg: pri 166, flags 17, from logserv.example.com,
    msg Dec 10 20:55:02 <syslog.err> logserv.example.com syslogd: exiting on signal 2
    cvthname(192.168.1.10)
    validate: dgram from IP 192.168.1.10, port 514, name logclient.example.com;
    accepted in rule 0.
    logmsg: pri 15, flags 0, from logclient.example.com, msg Dec 11 02:01:28 trhodes: Test message 2
    Logging to FILE /var/log/logclient.log
    Logging to FILE /var/log/messages

At this point, the messages are being properly received and placed in the correct file.

#### 11.7.3.4. 安全注意事項

As with any network service, security requirements should be considered before implementing a logging server. Log files may contain sensitive data about services enabled on the local host, user accounts, and configuration data. Network data sent from the client to the server will not be encrypted or password protected. If a need for encryption exists, consider using security/stunnel, which will transmit the logging data over an encrypted tunnel.

Local security is also an issue. Log files are not encrypted during use or after log rotation. Local users may access log files to gain additional insight into system configuration. Setting proper permissions on log files is critical. The built-in log rotator, newsyslog, supports setting permissions on newly created and rotated log files. Setting log files to mode `600` should prevent unwanted access by local users. Refer to newsyslog.conf(5) for additional information.

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