Home > Articles > Operating Systems, Server > Linux/UNIX/Open Source

Your Linux System

  • Print
  • + Share This

Reviewing the syslog.conf File

Now that we're happy with our inetd.conf file, let's take a quick look at our /etc/syslog.conf file. The standard syslog.conf is rather bland, and that's okay for many systems. But if you have a sensitive server, it just won't do.

Reviewing how a syslog.conf file is set up, let's take a look a some default entries:

daemon.alert                                            /var/log/alert
mail.*                                                  /var/log/mail
news.*                                                  /var/log/news.all
uucp,news.err                                           /var/log/spooler
authpriv.*;auth.*                                       /var/log/secure
*.info;news,mail,authpriv,auth.none                     -/var/log/messages
*.emerg                                                 *

I've rearranged the order of these lines taken from a default Caldera install after dropping all the comments and blank lines (easily done with grep: grep -v ^# /etc/syslog.conf | grep -v ^$). Let's talk about these entries so that we at least understand what's being logged where and when.

Log Entries

The first thing I want you to notice is that you have two columns separated by whitespace. The left column is the what, and the right column is the where. Most entries will be a write to a log. If you don't care that each log entry is immediately sync'd to disk, you can use a hyphen as the first character (as is done with the sixth entry here).

But "where" can be more than a file. A "where" can be a logged in a user or another system. A file must be full-pathed and so will start with a "/". A special case file would be something like /dev/console, where special handling is done for the console. A system user is shown by name, so it starts with an alphanumeric character. You can put in a comma-separated list of users, and syslog will send to any that are logged in. To send to everyone logged on, as in an emergency, you can use a "*". A remote system starts with an "@". Logging to remote systems is done via UDP. The usual problems accompany this type of logging: If you are under a denial-of-service attack and your network is saturated, the log messages may not make it to their destination. You may also log messages to a named pipe. The pipe that you want to use must exist before syslogd is started so that syslogd can attach to it. Named pipes will be listed in syslog.conf by preceding the full-pathed name with a "|" symbol.

By the way, a good insurance policy is to maintain your logs on a nonroot partition. If someone can force your logs to grow by triggering hundreds of syslog entries, and if your logs are on your root partition, you could wind up with a full root partition and a frozen system.

Priorities

Now let's turn our attention to the left column. This column is comprised of two parts, a facility and a priority. The two are separated with a ".". Looking at the first line in the sample previous syslog.conf file, you see daemon.alert. This means that with the daemon facility (more on facilities follows), all messages of alert or higher precedence are sent to /var/log/alerts.

Priorities are fairly simple. In descending order, they are as follows:

emerg (panic)
alert
crit
err (error)
warn (warning)
notice
info
debug

Alternate names for some priorities are shown in parenthesis. The priority names in parenthesis are deprecated and should not be used.

Specifying a particular priority specifies not only that priority, but all priorities above it by default. A comma-separated list of priorities is allowed. If you want only a particular priority but not priorities above it, you need to precede the priority with "=". You can also exclude a priority by prefacing it with "!". If you want to exclude just this priority, you can combine the two symbols, but the exclamation must come before the equal sign. Two priorities that syslog understands that are not listed are * and none, meaning "all" and "nothing," respectively.

The facility can be a comma-separated list of logging facilities. Facilities include these:

auth (security)
authpriv
cron
daemon
kern
lpr
mail
mark (for internal syslog use only)
news
syslog
user
uucp
local0–local7

For the most part, the facilities are self-explanatory. Those not obvious probably use one of the local facilities. For example, by convention, PPPD and chat use local2.

Looking again at our sample syslog.conf file, you can see that mail and news, regardless of the priority, all go to either /var/log/mail or /var/log/news. The next line shows that all messages of error priority or higher coming from UUCP or news go to /var/log/spool.

The next sample line shows that all priority authpriv and all priority auth messages go to /var/log/secure. So, you can see how to combine different selectors (facility.priority combinations) on the same line. They are separated by semicolons. In this case, because the priorities are both the same, it would be easier to write this as authpriv,auth.*.

The next line shows the power of the syslog selector line. First, we see that every facility, starting with priority info, is to be logged to /var/log/messages (buffered). Syslog expands the * and lists each facility. Following the semicolon, though, we have mail, news, auth, and authpriv listed, with a priority of none. This modifies the all facilities at info by removing mail, news, auth, and authpriv messages (because the priority none means just that—no messages). You can see from this line that what comes later modifies what came earlier.

Finally, any facility with an emergency message is broadcast to all logged in users.

That's it—it's really that easy. Just one final note: If you specify another system to receive messages (a central logging server, for example), that server's syslog daemon must be started with the -r option to bind the syslog UDP port. You'll want to take the precaution of using iptables to block unauthorized systems from sending you syslog messages so that someone can't flood your syslog server as part of an attack on systems on your network.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020