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3. Installing and Running Squid

3.1 How big of a system do I need to run Squid?

There are no hard-and-fast rules. The most important resource for Squid is physical memory. Your processor does not need to be ultra-fast. Your disk system will be the major bottleneck, so fast disks are important for high-volume caches. Do not use IDE disks if you can help it.

In late 1998, if you are buying a new machine for a cache, I would recommend the following configuration:

Your system disk, and logfile disk can probably be IDE without losing any cache performance.

Also, see Squid Sizing for Intel Platforms by Martin Hamilton This is a very nice page summarizing system configurations people are using for large Squid caches.

3.2 How do I install Squid?

After compiling Squid, you can install it with this simple command:

        % make install
If you have enabled the ICMP features then you will also want to type
        % su
        # make install-pinger

After installing, you will want to edit and customize the squid.conf file. By default, this file is located at /usr/local/squid/etc/squid.conf.

Also, a QUICKSTART guide has been included with the source distribution. Please see the directory where you unpacked the source archive.

3.3 What does the squid.conf file do?

The squid.conf file defines the configuration for squid. the configuration includes (but not limited to) HTTP port number, the ICP request port number, incoming and outgoing requests, information about firewall access, and various timeout information.

3.4 Do you have a squid.conf example?

Yes, after you make install, a sample squid.conf file will exist in the ``etc" directory under the Squid installation directory.

The sample squid.conf file contains comments explaining each option.

3.5 How do I start Squid?

First you need to make your Squid configuration. The Squid configuration can be found in /usr/local/squid/etc/squid.conf and by default includes documentation on all directives.

In the Suqid distribution there is a small QUICKSTART guide indicating which directives you need to look closer at and why. At a absolute minimum you need to change the http_access configuration to allow access from your clients.

To verify your configuration file you can use the -k parse option

        % /usr/local/squid/sbin/squid -k parse
If this outputs any errors then these are syntax errors or other fatal misconfigurations and needs to be corrected before you continue. If it is silent and immediately gives back the command promt then your squid.conf is syntactically correct and could be understood by Squid.

After you've finished editing the configuration file, you can start Squid for the first time. The procedure depends a little bit on which version you are using.

First, you must create the swap directories. Do this by running Squid with the -z option:

        % /usr/local/squid/sbin/squid -z

NOTE: If you run Squid as root then you may need to first create /usr/local/squid/var/logs and your cache_dir directories and assign ownership of these to the cache_effective_user configured in your squid.conf.

Once the creation of the cache directories completes, you can start Squid and try it out. Probably the best thing to do is run it from your terminal and watch the debugging output. Use this command:

        % /usr/local/squid/sbin/squid -NCd1
If everything is working okay, you will see the line:
        Ready to serve requests.
If you want to run squid in the background, as a daemon process, just leave off all options:
        % /usr/local/squid/sbin/squid

NOTE: depending on which http_port you select you may need to start squid as root (http_port <1024).

NOTE: In Squid-2.4 and earlier Squid was installed in bin by default, not sbin.

3.6 How do I start Squid automatically when the system boots?

Squid-2 has a restart feature built in. This greatly simplifies starting Squid and means that you don't need to use RunCache or inittab. At the minimum, you only need to enter the pathname to the Squid executable. For example:


Squid will automatically background itself and then spawn a child process. In your syslog messages file, you should see something like this:

        Sep 23 23:55:58 kitty squid[14616]: Squid Parent: child process 14617 started
That means that process ID 14563 is the parent process which monitors the child process (pid 14617). The child process is the one that does all of the work. The parent process just waits for the child process to exit. If the child process exits unexpectedly, the parent will automatically start another child process. In that case, syslog shows:
        Sep 23 23:56:02 kitty squid[14616]: Squid Parent: child process 14617 exited with status 1
        Sep 23 23:56:05 kitty squid[14616]: Squid Parent: child process 14619 started

If there is some problem, and Squid can not start, the parent process will give up after a while. Your syslog will show:

        Sep 23 23:56:12 kitty squid[14616]: Exiting due to repeated, frequent failures
When this happens you should check your syslog messages and cache.log file for error messages.

When you look at a process (ps command) listing, you'll see two squid processes:

        24353  ??  Ss     0:00.00 /usr/local/squid/bin/squid
        24354  ??  R      0:03.39 (squid) (squid)
The first is the parent process, and the child process is the one called ``(squid)''. Note that if you accidentally kill the parent process, the child process will not notice.

If you want to run Squid from your termainal and prevent it from backgrounding and spawning a child process, use the -N command line option.

        /usr/local/squid/bin/squid -N

From inittab

On systems which have an /etc/inittab file (Digital Unix, Solaris, IRIX, HP-UX, Linux), you can add a line like this:

        sq:3:respawn:/usr/local/squid/sbin/ < /dev/null >> /tmp/squid.log 2>&1
We recommend using a shell script, but you could instead call Squid directly with the -N option and other options you may require. A sameple script is shown below:
        export PATH TZ
        # User to notify on restarts

        # Squid command line options

        cd $C
        umask 022
        sleep 10
        while [ -f /var/run/nosquid ]; do
                sleep 1
        /usr/bin/tail -20 $C/logs/cache.log \
                | Mail -s "Squid restart on `hostname` at `date`" $notify
        exec bin/squid -N $opts

From rc.local

On BSD-ish systems, you will need to start Squid from the ``rc'' files, usually /etc/rc.local. For example:

        if [ -f /usr/local/squid/sbin/squid ]; then
                echo -n ' Squid'

From init.d

Squid ships with a init.d type startup script in contrib/squid.rc which works on most init.d type systems. Or you can write your own using any normal init.d script found in your system as template and add the start/stop fragments shown below.




        /usr/local/squid/sbin/squid -k shutdown
        while /usr/local/squid/sbin/squid -k check && [ $n -gt 120 ]; do
            sleep 1
            echo -n .
            n=`expr $n - 1`

3.7 How do I tell if Squid is running?

You can use the squidclient program:

        % squidclient > test

There are other command-line HTTP client programs available as well. Two that you may find useful are wget and echoping.

Another way is to use Squid itself to see if it can signal a running Squid process:

        % squid -k check
And then check the shell's exit status variable.

Also, check the log files, most importantly the access.log and cache.log files.

3.8 squid command line options

These are the command line options for Squid-2:


Specify an alternate port number for incoming HTTP requests. Useful for testing a configuration file on a non-standard port.


Debugging level for ``stderr'' messages. If you use this option, then debugging messages up to the specified level will also be written to stderr.


Specify an alternate squid.conf file instead of the pathname compiled into the executable.


Prints the usage and help message.

-k reconfigure

Sends a HUP signal, which causes Squid to re-read its configuration files.

-k rotate

Sends an USR1 signal, which causes Squid to rotate its log files. Note, if logfile_rotate is set to zero, Squid still closes and re-opens all log files.

-k shutdown

Sends a TERM signal, which causes Squid to wait briefly for current connections to finish and then exit. The amount of time to wait is specified with shutdown_lifetime.

-k interrupt

Sends an INT signal, which causes Squid to shutdown immediately, without waiting for current connections.

-k kill

Sends a KILL signal, which causes the Squid process to exit immediately, without closing any connections or log files. Use this only as a last resort.

-k debug

Sends an USR2 signal, which causes Squid to generate full debugging messages until the next USR2 signal is recieved. Obviously very useful for debugging problems.

-k check

Sends a ``ZERO'' signal to the Squid process. This simply checks whether or not the process is actually running.


Send debugging (level 0 only) message to syslog.


Specify an alternate port number for ICP messages. Useful for testing a configuration file on a non-standard port.


Prints the Squid version.


Creates disk swap directories. You must use this option when installing Squid for the first time, or when you add or modify the cache_dir configuration.


Do not make initial DNS tests. Normally, Squid looks up some well-known DNS hostnames to ensure that your DNS name resolution service is working properly.


If the swap.state logs are clean, then the cache is rebuilt in the ``foreground'' before any requests are served. This will decrease the time required to rebuild the cache, but HTTP requests will not be satisified during this time.


Do not automatically become a background daemon process.


Do not set the SO_REUSEADDR option on sockets.


Enable virtual host support for the httpd-accelerator mode. This is identical to writing httpd_accel_host virtual in the config file.


Enable full debugging while parsing the config file.


Return ICP_OP_MISS_NOFETCH instead of ICP_OP_MISS while the swap.state file is being read. If your cache has mostly child caches which use ICP, this will allow your cache to rebuild faster.

3.9 How do I see how Squid works?

3.10 Can Squid benefit from SMP systems?

Squid is a single process application and can not make use of SMP. If you want to make Squid benefit from a SMP system you will need to run multiple instances of Squid and find a way to distribute your users on the different Squid instances just as if you had multiple Squid boxes.

Having two CPUs is indeed nice for running other CPU intensive tasks on the same server as the proxy, such as if you have a lot of logs and need to run various statistics collections during peak hours.

The authentication and group helpers barely use any CPU and does not benefit from dual-CPU configuration.

3.11 Is it okay to use separate drives and RAID on Squid?

RAID1 is fine, and so are separate drives.

RAID0 (striping) with Squid only gives you the drawback that if you loose one of the drives the whole stripe set is lost. There is no benefit in performance as Squid already distributes the load on the drives quite nicely.

Squid is the worst case application for RAID5, whether hardware or software, and will absolutely kill the performance of a RAID5. Once the cache has been filled Squid uses a lot of small random writes which the worst case workload for RAID5, effectively reducing write speed to only little more than that of one single drive.

Generally seek time is what you want to optimize for Squid, or more precisely the total amount of seeks/s your system can sustain. Choosing the right RAID solution generally decreases the amount of seeks/s your system can sustain significantly.

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