Applies to openSUSE Leap 42.2

26 The Proxy Server Squid

Abstract

Squid is a widely-used proxy cache for Linux and Unix platforms. This means that it stores requested Internet objects, such as data on a Web or FTP server, on a machine that is closer to the requesting workstation than the server. It can be set up in multiple hierarchies to assure optimal response times and low bandwidth usage, even in modes that are transparent to end users. Additional software like squidGuard can be used to filter Web content.

Squid acts as a proxy cache. It redirects object requests from clients (in this case, from Web browsers) to the server. When the requested objects arrive from the server, it delivers the objects to the client and keeps a copy of them in the hard disk cache. An advantage of caching is that several clients requesting the same object can be served from the hard disk cache. This enables clients to receive the data much faster than from the Internet. This procedure also reduces the network traffic.

Along with actual caching, Squid offers a wide range of features:

  • Distributing load over intercommunicating hierarchies of proxy servers

  • Defining strict access control lists for all clients accessing the proxy

  • Allowing or denying access to specific Web pages using other applications

  • Generating statistics about frequently-visited Web pages for the assessment of surfing habits

Squid is not a generic proxy. It normally proxies only HTTP connections. It supports the protocols FTP, Gopher, SSL, and WAIS, but it does not support other Internet protocols, such as the news protocol, or video conferencing protocols. Because Squid only supports the UDP protocol to provide communication between different caches, many multimedia programs are not supported.

26.1 Some Facts about Proxy Caches

As a proxy cache, Squid can be used in several ways. When combined with a firewall, it can help with security. Multiple proxies can be used together. It can also determine what types of objects should be cached and for how long.

26.1.1 Squid and Security

It is possible to use Squid together with a firewall to secure internal networks from the outside using a proxy cache. The firewall denies all clients access to external services except Squid. All Web connections must be established by the proxy. With this configuration, Squid completely controls Web access.

If the firewall configuration includes a DMZ, the proxy should operate within this zone. Section 26.5, “Configuring a Transparent Proxy” describes how to implement a transparent proxy. This simplifies the configuration of the clients, because in this case, they do not need any information about the proxy.

26.1.2 Multiple Caches

Several instances of Squid can be configured to exchange objects between them. This reduces the total system load and increases the chances of retrieving an object from the local network. It is also possible to configure cache hierarchies, so a cache can forward object requests to sibling caches or to a parent cache—causing it to request objects from another cache in the local network or directly from the source.

Choosing the appropriate topology for the cache hierarchy is very important, because it is not desirable to increase the overall traffic on the network. For a very large network, it would make sense to configure a proxy server for every subnet and connect them to a parent proxy, which in turn is connected to the proxy cache of the ISP.

All this communication is handled by ICP (Internet cache protocol) running on top of the UDP protocol. Data transfers between caches are handled using HTTP (hypertext transmission protocol) based on TCP.

To find the most appropriate server from which to request objects, a cache sends an ICP request to all sibling proxies. The sibling proxies answer these requests via ICP responses. If the object was detected, they use the code HIT, if not, they use MISS.

If multiple HIT responses were found, the proxy server decides from which server to download, depending on factors such as which cache sent the fastest answer or which one is closer. If no satisfactory responses are received, the request is sent to the parent cache.

Note
Note: How Squid Avoids Duplication of Objects

To avoid duplication of objects in different caches in the network, other ICP protocols are used, such as CARP (cache array routing protocol) or HTCP (hypertext cache protocol). The more objects maintained in the network, the greater the possibility of finding the desired one.

26.1.3 Caching Internet Objects

Many objects available in the network are not static, such as dynamically generated pages and TLS/SSL-encrypted content. Objects like these are not cached because they change each time they are accessed.

To determine how long objects should remain in the cache, objects are assigned one of several states. Web and proxy servers find out the status of an object by adding headers to these objects, such as Last modified or Expires and the corresponding date. Other headers specifying that objects must not be cached can be used as well.

Objects in the cache are normally replaced, because of a lack of free disk space, using algorithms such as LRU (last recently used). This means that the proxy expunges those objects that have not been requested for the longest time.

26.2 System Requirements

System requirements largely depend on the maximum network load that the system must bear. Therefore, examine load peaks, as during those times, load might be more than four times the day's average. When in doubt, slightly overestimate the system's requirements. Having Squid working close to the limit of its capabilities can lead to a severe loss in quality of service. The following sections point to system factors in order of significance:

  1. RAM size

  2. CPU speed/physical CPU cores

  3. Size of the disk cache

  4. Hard disks/SSDs and their architecture

26.2.1 RAM

The amount of memory (RAM) required by Squid directly correlates with the number of objects in the cache. Random access memory is much faster than a hard disk/SSD. Therefore, it is very important to have sufficient memory for the Squid process, because system performance is dramatically reduced if it must be swapped to disk.

Squid also stores cache object references and frequently requested objects in the main memory to speed up retrieval of this data. In addition to that, there is other data that Squid needs to keep in memory, such as a table with all the IP addresses handled, an exact domain name cache, the most frequently requested objects, access control lists, buffers, and more.

26.2.2 CPU

Squid is tuned to work best with lower processor core counts (4–8 physical cores), with each providing high performance. Technologies providing virtual cores such as hyperthreading can hurt performance.

To make the best use of multiple CPU cores, it is necessary to set up multiple worker threads writing to different caching devices. By default, multi-core support is mostly disabled.

26.2.3 Size of the Disk Cache

In a small cache, the probability of a HIT (finding the requested object already located there) is small, because the cache is easily filled and less requested objects are replaced by newer ones. If, for example, 1 GB is available for the cache and the users use up only 10 MB per day surfing, it would take more than one hundred days to fill the cache.

The easiest way to determine the necessary cache size is to consider the maximum transfer rate of the connection. With a 1 Mbit/s connection, the maximum transfer rate is 128 KB/s. If all this traffic ended up in the cache, in one hour it would add up to 460 MB. Assuming that all this traffic is generated in only eight working hours, it would reach 3.6 GB in one day. Because the connection is normally not used to its upper volume limit, it can be assumed that the total data volume handled by the cache is approximately 2 GB. Hence, in this example, 2 GB of disk space is required for Squid to keep one day's worth of browsing data cached.

26.2.4 Hard Disk/SSD Architecture

Speed plays an important role in the caching process, so this factor deserves special attention. For hard disks/SSDs, this parameter is described as random seek time or random read performance, measured in milliseconds. Because the data blocks that Squid reads from or writes to the hard disk/SSD tend to be small, the seek time/read performance of the hard disk/SSD is more important than its data throughput.

For use as a proxy, hard disks with high rotation speeds or SSDs are the best choice. When using hard disks, it can be better to use multiple smaller hard disks, each with a single cache directory to avoid excessive read times.

Using a RAID system allows increasing reliability at expense of speed. However, for performance reasons, avoid (software) RAID5 and similar settings.

File system choice is usually not decisive. However, using the mount option noatime can improve performance—Squid provides its own time stamps and thus does not need the file system to track access times.

26.3 Basic Usage of Squid

If not already installed, install the package squid . squid is not among the packages installed by default on openSUSE® Leap.

Squid is already preconfigured in openSUSE Leap, you can start it directly after the installation. To ensure a smooth start-up, the network should be configured in a way that at least one name server and the Internet can be reached. Problems can arise if a dial-up connection is used with a dynamic DNS configuration. In this case, at least the name server should be specified, because Squid does not start if it does not detect a DNS server in /etc/resolv.conf.

26.3.1 Starting Squid

To start Squid, use:

tux > sudo systemctl start squid

If you want Squid to start together with the system, enable the service with systemctl enable squid.

26.3.2 Checking Whether Squid Is Working

To check whether Squid is running, choose one of the following ways:

  • Using systemctl:

    tux > systemctl start squid

    The output of this command should indicate that Squid is loaded and active (running).

  • Using Squid itself:

    tux > sudo squid -k | echo $?

    The output of this command should be 0, without further messages.

To test the functionality of Squid on the local system, choose one of the following ways:

  • To test, you can use squidclient, a command-line tool that can output the response to a Web request, similar to wget or curl.

    Unlike those tools, squidclient will automatically connect to the default proxy setup of Squid, localhost:3128. However, if you changed the configuration of Squid, you need to configure squidclient to use different settings using command line options. For more information, see squidclient --help.

    Example 26.1: A Request With squidclient
    tux > squidclient http://www.example.org
    HTTP/1.1 200 OK
    Cache-Control: max-age=604800
    Content-Type: text/html
    Date: Fri, 22 Jun 2016 12:00:00 GMT
    Expires: Fri, 29 Jun 2016 12:00:00 GMT
    Last-Modified: Fri, 09 Aug 2013 23:54:35 GMT
    Server: ECS (iad/182A)
    Vary: Accept-Encoding
    X-Cache: HIT
    x-ec-custom-error: 1
    Content-Length: 1270
    X-Cache: MISS from moon1
    X-Cache-Lookup: MISS from moon:3128
    Via: 1.1 moon (squid/3.5.16)2
    Connection: close
    
    <!doctype html>
    <html>
    <head>
        <title>Example Domain</title>
    [...]
    </body>
    </html>

    The output shown in Example 26.1, “A Request With squidclient can be split into two parts:

    1. The protocol headers of the response: the lines before the blank line.

    2. The actual content of the response: the lines after the blank line.

    To verify that Squid is used, refer to the selected header lines:

    1

    The value of the header X-Cache tells you that the requested document was not in the Squid cache (MISS) of the computer moon.

    The example above contains two X-Cache lines. You can ignore the first X-Cache header. It is produced by the internal caching software of the originating Web server.

    2

    The value of the header Via tells you the HTTP version, the name of the computer, and the version of Squid in use.

  • Using a browser: Set up localhost as the proxy and 3128 as the port. You can then load a page and check the response headers in the Network panel of the browser's Inspector or Developer Tools. The headers should be reproduced similarly to the way shown in Example 26.1, “A Request With squidclient.

To allow users from the local system and other systems to access Squid and the Internet, change the entry in the configuration files /etc/squid/squid.conf from http_access deny all to http_access allow all. However, in doing so, consider that Squid is made completely accessible to anyone by this action. Therefore, define ACLs (access control lists) that control access to the proxy. After modifying the configuration file, Squid must be reloaded or restarted. For more information on ACLs, see Section 26.4.2, “Options for Access Controls”.

If Squid dies after a short period of time even though it was started successfully, check whether there is a faulty name server entry or whether the /etc/resolv.conf file is missing. Squid logs the cause of a start-up failure in the file /var/log/squid/cache.log.

26.3.3 Stopping, Reloading, and Restarting Squid

Do this with systemctl reload squid. Alternatively, completely restart Squid with systemctl restart squid.

The command systemctl stop squid causes Squid to shut down. This can take a while, because Squid waits up to half a minute (shutdown_lifetime option in /etc/squid/squid.conf) before dropping the connections to the clients and writing its data to the disk.

Warning
Warning: Terminating Squid

Terminating Squid with kill or killall can damage the cache. To be able to restart Squid, damaged caches must be deleted.

26.3.4 Removing Squid

Removing Squid from the system does not remove the cache hierarchy and log files. To remove these, delete the /var/cache/squid directory manually.

26.3.5 Local DNS Server

Setting up a local DNS server makes sense even if it does not manage its own domain. It then simply acts as a caching-only name server and is also able to resolve DNS requests via the root name servers without requiring any special configuration (see Section 19.4, “Starting the BIND Name Server”). How this can be done depends on whether you chose dynamic DNS during the configuration of the Internet connection.

Dynamic DNS

Normally, with dynamic DNS, the DNS server is set by the provider during the establishment of the Internet connection and the local /etc/resolv.conf file is adjusted automatically. This behavior is controlled in the /etc/sysconfig/network/config file with the NETCONFIG_DNS_POLICY sysconfig variable. Set NETCONFIG_DNS_POLICY to "" with the YaST sysconfig editor.

Then, add the local DNS server in the /etc/resolv.conf file with the IP address 127.0.0.1 for localhost. This way, Squid can always find the local name server when it starts.

To make the provider's name server accessible, specify it in the configuration file /etc/named.conf under forwarders along with its IP address. With dynamic DNS, this can be achieved automatically when establishing the connection by setting the sysconfig variable NETCONFIG_DNS_POLICY to auto.

Static DNS

With static DNS, no automatic DNS adjustments take place while establishing a connection, so there is no need to change any sysconfig variables. However, you must specify the local DNS server in the file /etc/resolv.conf as described in Dynamic DNS. Additionally, the provider's static name server must be specified manually in the /etc/named.conf file under forwarders along with its IP address.

Tip
Tip: DNS and Firewall

If you have a firewall running, make sure DNS requests can pass it.

26.4 The /etc/squid/squid.conf Configuration File

All Squid proxy server settings are made in the /etc/squid/squid.conf file. To start Squid for the first time, no changes are necessary in this file, but external clients are initially denied access. The proxy is available for localhost. The default port is 3128. The preinstalled configuration file /etc/squid/squid.conf provides detailed information about the options and many examples.

Many entries are commented and therefore begin with the comment character #. The relevant specifications can be found at the end of the line. The given values usually correlate with the default values, so removing the comment signs without changing any of the parameters usually has no effect. If possible, leave the commented lines as they are and insert the options along with the modified values in the line below. This way, the default values may easily be recovered and compared with the changes.

Tip
Tip: Adapting the Configuration File After an Update

If you have updated from an earlier Squid version, it is recommended to edit the new /etc/squid/squid.conf and only apply the changes made in the previous file.

Sometimes, Squid options are added, removed, or modified. Therefore, if you try to use the old squid.conf, Squid might stop working properly.

26.4.1 General Configuration Options

The following is a list of a selection of configuration options for Squid. It is not exhaustive. The Squid package contains a full, lightly documented list of options in /etc/squid/squid.conf.documented.

http_port PORT

This is the port on which Squid listens for client requests. The default port is 3128, but 8080 is also common.

cache_peer HOST_NAME TYPE PROXY_PORT ICP_PORT

This option allows creating a network of caches that work together. The cache peer is a computer that also hosts a network cache and stands in a relationship to your own. The type of relationship is specified as the TYPE. The type can either be parent or sibling.

As the HOST_NAME, specify the name or IP address of the proxy to use. For PROXY_PORT, specify the port number for use in a browser (usually 8080). Set ICP_PORT to 7 or, if the ICP port of the parent is not known and its use is irrelevant to the provider, to 0.

To make Squid behave like a Web browser instead of like a proxy, prohibit the use of the ICP protocol. You can do so by appending the options default and no-query.

cache_mem SIZE

This option defines the amount of memory Squid can use for very popular replies. The default is 8 MB. This does not specify the memory usage of Squid and may be exceeded.

cache_dir STORAGE_TYPE CACHE_DIRECTORY CACHE_SIZE LEVEL_1_DIRECTORIES LEVEL_2_DIRECTORIES

The option cache_dir defines the directory for the disk cache. In the default configuration on openSUSE Leap, Squid does not create a disk cache.

The placeholder STORAGE_TYPE can be one of the following:

  • Directory-based storage types: ufs, aufs (the default), diskd. All three are variations of the storage format ufs. However, while ufs runs as part of the core Squid thread, aufs runs in a separate thread, and diskd uses a separate process. This means that the latter two types avoid blocking Squid because of disk I/O.

  • Database-based storage systems: rock. This storage format relies on a single database file, in which each object takes up one or more memory units of a fixed size (slots).

In the following, only the parameters for storage types based on ufs will be discussed. rock has somewhat different parameters.

The CACHE_DIRECTORY is the directory for the disk cache. By default, that is /var/cache/squid. CACHE_SIZE is the maximum size of that directory in megabytes; by default, this is set to 100 MB. Set it to between 50% and a maximum of 80% of available disk space.

The final two values, LEVEL_1_DIRECTORIES and LEVEL_2_DIRECTORIES specify how many subdirectories are created in the CACHE_DIRECTORY. By default, 16 subdirectories are created at the first level below CACHE_DIRECTORY and 256 within each of these. These values should only be increased with caution, because creating too many directories can lead to performance problems.

If you have several disks that share a cache, specify several cache_dir lines.

cache_access_log LOG_FILE , cache_log LOG_FILE , cache_store_log LOG_FILE

These three options specify the paths where Squid logs all its actions. Normally, nothing needs to be changed here. If Squid is burdened by heavy usage, it might make sense to distribute the cache and the log files over several disks.

client_netmask NETMASK

This option allows masking IP addresses of clients in the log files by applying a subnet mask. For example, to set the last digit of the IP address to 0, specify 255.255.255.0.

ftp_user E-MAIL

This option allows setting the password that Squid should use for anonymous FTP login. Specify a valid e-mail address here, because some FTP servers check these for validity.

cache_mgr E-MAIL

If it unexpectedly crashes, Squid sends a message to this e-mail address. The default is webmaster.

logfile_rotate VALUE

If you run squid -k rotate, Squid can rotate log files. The files are numbered in this process and, after reaching the specified value, the oldest file is overwritten. The default value is 10 which rotates log files with the numbers 0 to 9.

However, on openSUSE Leap, rotating log files is performed automatically using logrotate and the configuration file /etc/logrotate.d/squid.

append_domain DOMAIN

Use append_domain to specify which domain to append automatically when none is given. Usually, your own domain is specified here, so specifying www in the browser accesses your own Web server.

forwarded_for STATE

If this option is set to on, it adds a line to the header similar to this:

X-Forwarded-For: 192.168.0.1

If you set this option to off, Squid removes the IP address and the system name of the client from HTTP requests.

negative_ttl TIME , negative_dns_ttl TIME

If these options are set, Squid will cache some types of failures, such as 404 responses. It will then refuse to issue new requests, even if the resource would be available then.

By default, negative_ttl is set to 0, negative_dns_ttl is set to 1 minutes. This means that negative responses to Web requests are not cached by default, while negative responses to DNS requests are cached for 1 minute.

never_direct allow ACL_NAME

To prevent Squid from taking requests directly from the Internet, use the option never_direct to force connection to another proxy. This must have previously been specified in cache_peer. If all is specified as the ACL_NAME, all requests are forwarded directly to the parent. This can be necessary, for example, if you are using a provider that dictates the use of its proxies or denies its firewall direct Internet access.

26.4.2 Options for Access Controls

Squid provides a detailed system for controlling the access to the proxy. These Access Control Lists (ACL) are lists with rules that are processed sequentially. ACLs must be defined before they can be used. Some default ACLs, such as all and localhost, already exist. However, the mere definition of an ACL does not mean that it is actually applied. This only happens when there is a corresponding http_access rule.

The syntax for the option acl is as follows:

acl ACL_NAME TYPE DATA

The placeholders within this syntax stand for the following:

  • The name ACL_NAME can be chosen arbitrarily.

  • For TYPE, select from a variety of different options which can be found in the ACCESS CONTROLS section in the /etc/squid/squid.conf file.

  • The specification for DATA depends on the individual ACL type and can also be read from a file. For example, via host names, IP addresses, or URLs.

For more information on types of ACL rules, see the Squid documentation at http://www.squid-cache.org/Versions/v3/3.5/cfgman/acl.html.

Example 26.2: Defining ACL Rules
acl mysurfers srcdomain .example.com 1
acl teachers src 192.168.1.0/255.255.255.0 2
acl students src 192.168.7.0-192.168.9.0/255.255.255.0 3
acl lunch time MTWHF 12:00-15:00 4

1

This ACL defines mysurfers to be all users coming from within .example.com (as determined by a reverse lookup for the IP).

2

This ACL defines teachers to be the users of computers with IP addresses starting with 192.168.1..

3

This ACL defines students to be the users of the computer with IP addresses starting with 192.168.7., 192.168.8., or 192.168.9..

4

This ACL defines lunch, as a time on the days Monday, Tuesday, ... Friday between noon and 3 p.m.

http_access allow ACL_NAME

http_access defines who is allowed to use the proxy and who can access what on the Internet. For this, ACLs must be defined. localhost and all have already been defined above for which you can deny or allow access via deny or allow. A list containing any number of http_access entries can be created, processed from top to bottom. Depending on which occurs first, access is allowed or denied to the respective URL. The last entry should always be http_access deny all. In the following example, localhost has free access to everything while all other hosts are denied access completely:

http_access allow localhost
http_access deny all

In another example using these rules, the group teachers always has access to the Internet. The group students only has access between Monday and Friday during lunch time:

http_access deny localhost
http_access allow teachers
http_access allow students lunch time
http_access deny all

For readability, within the configuration file /etc/squid/squid.conf, specify all http_access options as a block.

url_rewrite_program PATH

With this option, specify a URL rewriter. For example, this can be squidGuard (/usr/sbin/squidGuard) which allows blocking unwanted URLs. With it, Internet access can be individually controlled for various user groups using proxy authentication and the appropriate ACLs.

For more information on squidGuard, see Section 26.7, “squidGuard”.

auth_param basic program PATH

If users must be authenticated on the proxy, set a corresponding program, such as /usr/sbin/pam_auth. When accessing pam_auth for the first time, the user sees a login window in which they need to specify a user name and a password. In addition, you need an ACL, so only clients with a valid login can use the Internet:

acl password proxy_auth REQUIRED

http_access allow password
http_access deny all

In the acl proxy_auth option, using REQUIRED means that all valid user names are accepted. REQUIRED can also be replaced with a list of permitted user names.

ident_lookup_access allow ACL_NAME

With this option, have an ident request run to find each user's identity for all clients defined by an ACL of the type src. Alternatively, use this for all clients, apply the predefined ACL all as the ACL_NAME.

All clients covered by ident_lookup_access must run an ident daemon. On Linux, you can use pidentd (package pidentd ) as the ident daemon. For other operating systems, free software is usually available. To ensure that only clients with a successful ident lookup are permitted, define a corresponding ACL:

acl identhosts ident REQUIRED

http_access allow identhosts
http_access deny all

In the acl identhosts ident option, using REQUIRED means that all valid user names are accepted. REQUIRED can also be replaced with a list of permitted user names.

Using ident can slow down access time, because ident lookups are repeated for each request.

26.5 Configuring a Transparent Proxy

The usual way of working with proxy servers is the following: the Web browser sends requests to a certain port of the proxy server and the proxy always provides these required objects, regardless of whether they are in its cache. However, in some cases the transparent proxy mode of Squid makes sense:

  • If, for security reasons, it is recommended that all clients use a proxy to surf the Internet.

  • If all clients must use a proxy, regardless of whether they are aware of it.

  • If the proxy in a network is moved, but the existing clients need to retain their old configuration.

A transparent proxy intercepts and answers the requests of the Web browser, so the Web browser receives the requested pages without knowing where they are coming from. As the name indicates, the entire process is transparent to the user.

Procedure 26.1: Squid as a Transparent Proxy
  1. In /etc/squid/squid.conf, on the line of the option http_port add the parameter transparent:

    http_port 3128 transparent
  2. Restart Squid:

    tux > sudo systemctl restart squid
  3. Set up SuSEFirewall2 to redirect HTTP traffic to the port given in http_proxy (in the example above, that was port 3128). To do so, edit the configuration file /etc/sysconfig/SuSEfirewall2.

    This example assumes that you are using the following devices:

    • Device pointing to the Internet: FW_DEV_EXT="eth1"

    • Device pointing to the network: FW_DEV_INT="eth0"

    Define ports and services (see /etc/services) on the firewall that are accessed from untrusted (external) networks such as the Internet. In this example, only Web services are offered to the outside:

    FW_SERVICES_EXT_TCP="www"

    Define ports or services (see /etc/services) on the firewall that are accessed from the secure (internal) network, both via TCP and UDP:

    FW_SERVICES_INT_TCP="domain www 3128"
    FW_SERVICES_INT_UDP="domain"

    This allows accessing Web services and Squid (whose default port is 3128). The service domain stands for DNS (domain name service). This service is commonly used. Otherwise, simply remove domain from the above entries and set the following option to no:

    FW_SERVICE_DNS="yes"

    The option FW_REDIRECT is very important, as it is used for the actual redirection of HTTP traffic to a specific port. The configuration file explains the syntax in a comment above the option:

    # Format:
    # list of <source network>[,<destination network>,<protocol>[,dport[:lport]]
    # Where protocol is either tcp or udp. dport is the original
    # destination port and lport the port on the local machine to
    # redirect the traffic to
    #
    # An exclamation mark in front of source or destination network
    # means everything EXCEPT the specified network

    That is:

    1. Specify the IP address and the netmask of the internal networks accessing the proxy firewall.

    2. Specify the IP address and the netmask to which these clients send their requests. In the case of Web browsers, specify the networks 0/0, a wild card that means to everywhere.

    3. Specify the original port to which these requests are sent.

    4. Specify the port to which all these requests are redirected. In the example below, only Web services (port 80) are redirected to the proxy port (port 3128). If there are more networks or services to add, separate them with a space in the respective entry.

      Because Squid supports protocols other than HTTP, you can also redirect requests from other ports to the proxy. For example, you can also redirect port 21 (FTP) and port 443 (HTTPS or SSL).

    Therefore, for a Squid configuration, you could use:

    FW_REDIRECT="192.168.0.0/16,0/0,tcp,80,3128"
  4. In the configuration file /etc/sysconfig/SuSEfirewall2, make sure that the entry START_FW is set to "yes".

  5. Restart SuSEFirewall2:

    tux > sudo systemctl restart SuSEfirewall2
  6. To verify that everything is working properly, check the Squid log files in /var/log/squid/access.log. To verify that all ports are correctly configured, perform a port scan on the machine from any computer outside your network. Only the Web services (port 80) should be open. To scan the ports with nmap, use:

    nmap -O IP_ADDRESS

26.6 Using the Squid Cache Manager CGI Interface (cachemgr.cgi)

The Squid cache manager CGI interface (cachemgr.cgi) is a CGI utility for displaying statistics about the memory usage of a running Squid process. It is also a convenient way to manage the cache and view statistics without logging the server.

Procedure 26.2: Setting up cachemgr.cgi
  1. Make sure the Apache Web server is running on your system. Configure Apache as described in Chapter 24, The Apache HTTP Server. In particular, see Section 24.5, “Enabling CGI Scripts”. To check whether Apache is already running, use:

    tux > sudo systemctl status apache2

    If inactive is shown, you can start Apache with the openSUSE Leap default settings:

    tux > sudo systemctl start apache2
  2. Now enable cachemgr.cgi in Apache. To do so, create a configuration file for a ScriptAlias.

    Create the file in the directory /etc/apache2/conf.d and name it cachemgr.conf. In it, add the following:

    ScriptAlias /squid/cgi-bin/ /usr/lib64/squid/
    
    <Directory "/usr/lib64/squid/">
    Options +ExecCGI
    AddHandler cgi-script .cgi
    Require host HOST_NAME
    </Directory>

    Replace HOST_NAME with the host name of the computer you want to access cachemgr.cgi from. This allows only your computer to access cachemgr.cgi. To allow access from anywhere, use Require all granted instead.

    • If Squid and your Apache Web server run on the same computer, there should be no changes that need to be made to /etc/squid/squid.conf. However, verify that /etc/squid/squid.conf contains the following lines:

        http_access allow manager localhost
        http_access deny manager

      These lines allow you to access the manager interface from your own computer (localhost) but not from elsewhere.

    • If Squid and your Apache Web server run on different computers, you need to add extra rules to allow access from the CGI script to Squid. Define an ACL for your server (replace WEB_SERVER_IP with the IP address of your Web server):

      acl webserver src WEB_SERVER_IP/255.255.255.255

      Make sure the following rules are in the configuration file. Compared to the default configuration, only the rule in the middle is new. However, the sequence is important.

      http_access allow manager localhost
      http_access allow manager webserver
      http_access deny manager
  3. Optionally, you can configure one or more passwords for cachemgr.cgi. This also allows access to more actions such as closing the cache remotely or viewing more information about the cache. For this, configure the options cache_mgr and cachemgr_passwd with one or more password for the manager and a list of allowed actions.

    For example, to explicitly enable viewing the index page, the menu, 60-minute average of counters without authentication, to enable toggling offline mode using the password secretpassword, and to completely disable everything else, use the following configuration:

    cache_mgr user
    cachemgr_passwd none index menu 60min
    cachemgr_passwd secretpassword offline_toggle
    cachemgr_passwd disable all

    cache_mgr defines a user name. cache_mgr defines which actions are allowed using which password.

    The keywords none and disable are special: none removes the need for a password, disable disables functionality outright.

    The full list of actions can be best seen after logging in to cachemgr.cgi. To find out how the operation needs to be referenced in the configuration file, see the string after &operation= in the URL of the action page. all is a special keyword meaning all actions.

  4. Reload Squid and Apache after the configuration file changes:

    tux > sudo systemctl reload squid
  5. To view the statistics, go to the cachemgr.cgi page that you set up before. For example, it could be http://webserver.example.org/squid/cgi-bin/cachemgr.cgi.

    Choose the right server, and, if set, specify user name and password. Then click Continue and browse through the different statistics.

26.7 squidGuard

This section is not intended to explain an extensive configuration of squidGuard, only to introduce it and give some advice for using it. For more in-depth configuration issues, refer to the squidGuard Web site at http://www.squidguard.org.

squidGuard is a free (GPL), flexible, and fast filter, redirector, and access controller plug-in for Squid. It lets you define multiple access rules with different restrictions for different user groups on a Squid cache. squidGuard uses Squid's standard redirector interface. squidGuard can do the following:

  • Limit Web access for some users to a list of accepted or well-known Web servers or URLs.

  • Block access to some listed or blacklisted Web servers or URLs for some users.

  • Block access to URLs matching a list of regular expressions or words for some users.

  • Redirect blocked URLs to an intelligent CGI-based information page.

  • Redirect unregistered users to a registration form.

  • Redirect banners to an empty GIF.

  • Use different access rules based on time of day, day of the week, date, etc.

  • Use different rules for different user groups.

squidGuard and Squid cannot be used to:

  • Edit, filter, or censor text inside documents.

  • Edit, filter, or censor HTML-embedded scripts such as JavaScript.

Procedure 26.3: Setting Up squidGuard
  1. Before it can be used, install squidGuard .

  2. Provide a minimal configuration file as /etc/squidguard.conf. Find configuration examples in http://www.squidguard.org/Doc/examples.html. Experiment later with more complicated configuration settings.

  3. Next, create an access denied HTML page or CGI page that Squid can redirect to if the client requests a blacklisted Web site. Using Apache is strongly recommended.

  4. Now, configure Squid to use squidGuard. Use the following entry in the /etc/squid/squid.conf file:

    redirect_program /usr/bin/squidGuard
  5. Another option called redirect_children configures the number of redirect (in this case squidGuard) processes running on the machine. The more processes you set, the more RAM is required. Try low numbers first, for example, 4:

    redirect_children 4
  6. Last, have Squid load the new configuration by running systemctl reload squid. Now, test your settings with a browser.

26.8 Cache Report Generation with Calamaris

Calamaris is a Perl script used to generate reports of cache activity in ASCII or HTML format. It works with native Squid access log files. The Calamaris home page is located at http://cord.de/calamaris-english. This tool does not belong to the openSUSE Leap default installation scope—to use it, install the calamaris package.

Log in as root, then enter:

cat access1.log [access2.log access3.log] | calamaris options > reportfile

When using more than one log file, make sure they are chronologically ordered, with older files listed first. This can be achieved by either listing the files one after the other as in the example above, or by using access{1..3}.log.

calamaris takes the following options:

-a

output all available reports

-w

output as HTML report

-l

include a message or logo in report header

More information about the various options can be found in the program's manual page with man calamaris.

A typical example is:

cat access.log.{10..1} access.log | calamaris -a -w \
> /usr/local/httpd/htdocs/Squid/squidreport.html

This puts the report in the directory of the Web server. Apache is required to view the reports.

26.9 For More Information

Visit the home page of Squid at http://www.squid-cache.org/. Here, find the Squid User Guide and a very extensive collection of FAQs on Squid.

In addition, mailing lists are available for Squid at http://www.squid-cache.org/Support/mailing-lists.html.

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