Understanding Squid Proxy Logs and How to View Logs

Understanding Squid Proxy Logs and How to View Logs. Are you looking for a way to analyze your squid proxy logs in real time? Not sure how to get started? If so, understanding squid proxy logs and viewing them is a daunting tasks for even experienced network administrators. However, an ever increasing number of users rely on open source proxy servers that require access logging as part of standard security policy.

In this blog post, we take a closer look at squid log details and uncover several methods used to view Squid log analyses over time. In addition, you gain insight into each element in the Squid log and learn some ways to troubleshoot issues using Squid log data. For example, determining the types of HTTP requests sent by visitors or crafting more secure filters with greater accuracy.

Let’s continue reading Understanding Squid Proxy Logs and How to View Logs.

What are Squid Proxy Logs?

Squid proxy logs are used to store information about requests made by clients to the web server. This log contains the source IP address, the destination URL, and other metadata about the request. The log provides information about how visitors use a website or network, what kind of traffic is requested, and if any malicious activities are occurring.

Network administrators need to understand the log fields and how they are interpreted to troubleshoot problems effectively and monitor traffic. In effect, the log also provides an audit trail that is used to identify and block requests from malicious sources.

How to view Logs

There are a variety of ways to view squid logs, depending on the level of detail you need and how quickly you need to access the log data.

A web based interface is the most popular and straightforward way to view squid logs. This graphical user interface (GUI) makes it easy to quickly search and filter the log data. For example, administrators only view requests from a specific IP address or use wildcards to find more general patterns.

Hence, a command line interface is used, if you require a more sophisticated way to analyse squid logs. in nutshell, an ideal scenario for situations where you need to dig deeper into the data or have greater control over the log analysis. With the command line interface, administrators pipe the log data through various commands to find information such as the most requested URLs, user agent strings and more.

1. Display log files in real-time

All in all, the tail command is a helpful tool for viewing Squid log files in real time. This command monitors Squid log, as requests are made and received. The tail command also filters log data, so that only certain requests are shown in the output. For example, you use the tail command to view only requests from a certain IP address or look for specific user agent strings.

2. Search log files

The grep a command is a powerful tool for searching Squid log files. With it, you search through the entire log file or just a specific portion of it. For example, you use grep to search for particular source IP addresses or user agent strings. Additionally, the grep command filters out any undesired content from the log data.

3. View log files

The less command is a great way to view Squid log files. This command allows you to page through the log data one line at a time or jump to a specific section. Additionally, you also use less control to filter log data by searching for strings or IP addresses.

/var/log/squid/ log file directory

Keeping an eye on the logs might provide essential details about the usage and efficiency of Squid. Besides, Data like internal storage use, as well as setup issues, are also kept in the logs. Above all, Squid has many log files for different purposes. Some must be enabled explicitly at compilation time, while others may be securely disabled.


Here, any signals Squid produces, whether experimental or failure, is sent to the cache.log file. In addition, squid then sends a copy of some events to your Syslog services, if you begin the process by running the RunCache program or by specifying the -s command on the operating system. Keeping the squid log information in a standalone executable is optional.


All items, whether they are still on disk or have been deleted, are documented in store.log. This is a form of digital ledger used mostly for testing and troubleshooting.

Only by analysing the whole log file you say with certainty whether or not an item is stored on your drives. Sometimes the change out uses this to disk occurs after the update removal of an item has been recorded.


Importantly, most log file statistical packages use the data in access.log. This file may be used to learn details about the squid server’s users, such as which IP addresses they are connecting, which URLs they visit, and so on.

How to Use Tail Command?

Well, the tail command is used to view the last lines of a file. Use it to view log files in real time, or to filter log data by specific strings.

To view the last 10 lines of a file, you use the following command:

tail -n 10 log_file_name.log

To view the last line of a file, use the following command:

tail -n 1 log_file_name.log

Also use the tail command to filter specific strings from a file. For example, to view only requests from a specific IP address, use the following command:

tail -f log_file_name.log | grep “ip_address”

In order to view only requests with a specific user agent string, you use the following command:

tail -f log_file_name.log | grep “user-agent_string”

How to Use Grep Command to Search?

In detail, the grep command is used to search through the Squid log files. To use the command, enter ‘grep‘ followed by a string or pattern to search for, followed by the log file you wish to search in. In essence, if you wanted to search the access.log file for a particular IP address, you would type ‘grep <IP address> /var/log/squid/access.log‘.

If a match is found, the command returns the matching line. If no matches are found, grep simply exits without returning any output. Additionally, you use various flags with the grep command to further refine your search.

Subsequently, by using the tail, grep, and less commands, administrators easily view, search, and analyse their Squid log files. This is extremely helpful for troubleshooting issues, monitoring user activity, and gaining insights into system performance. With these commands, administrators quickly and easily gain insight into the Squid logs and ensure their system is running as efficiently as possible.

The grep command scans the whole file for the provided pattern. It’s used by entering grep followed by the regular expression and the document’s name. In this case, the three parts in the file containing the word “not” are what we’re looking for.

How to Use the Control Filter?

In like fashion, control filtering is another way of searching a Squid log file. In other words, it allows you to filter the logs by certain conditions, such as IP addresses, user agent strings, HTTP response codes, etc. To use the control filter, enter ‘less -f <filename>‘ followed by a plus sign and a set of conditions.

The terminal window displays all lines that match the provided conditions. In particular, if you wanted to only view lines in the access.log file that contain an IP address of, you would enter ‘less -f /var/log/squid/access.log +pattern ““‘.

Warnings and Messages from Squid

There is more than one kind of error code. Neither level 0 nor level 1 debug traces are recorded. Management communications of the highest priority are only broadcast here.

For whatever reason, the Squid program has terminated with a FATAL error message influencing all active clients receiving traffic from that Squid server. Such issues must be fixed before Squid may be executed if they arise during startup or configuration.

If a client receives an ERROR message, a critical error has occurred during an operation, which may have knock on effect for other clients. However, it hasn’t halted all traffic operations.

These are also possible during the Squid start up and configuration processes. So, until the issue is fixed and Squid is rebuilt, no operational processes that rely on that module occur.

SECURITY ERROR messages indicate problems processing a client request with the security controls which Squid has configured with. Some impossible condition is required to pass the security test. This is commonly seen when testing whether to accept a client request based on some reply detail that are only be available in the future.

SECURITY ALERT messages indicate security attack problems being detected. This is only for unambiguous problems. ‘Attacks’ signatures that can appear in normal traffic are logged as regular WARNING.

Therefore protection issues with the setup setting may trigger SECURITY NOTICE notifications on installation and reconfiguration. These are followed by recommendations for improving the setup and an explanation of what operation Squid takes in place of the one specified by the user.

Which Logs Shouldn't I Worry About Deleting?

The log files access.log, store.log, and cache.log must never be deleted while Squid is active. UNIX allows the deletion of files even if another program is using them. However, till the application that created the file terminates, the disk space is not returned.

If, while Squid is operating, you erase the swap.state by mistake, you may restore it by adhering to the steps outlined in the preceding FAQs. However, in case you remove the others once Squid is active, you will not be able to get them back.

Undoubtedly, log files should be rotated regularly using Squid’s rotate function. If you’re not rotating your log files daily, you should start. After the existing log files are deleted, they are given new names that end in numbers. 0, .1, etc. In order to erase or store the old application logs, you may create your programs if you so wish. If you don’t set logfile to rotate, Squid only stores the most recent log file rotate updates. Furthermore, the logfile rotation process creates a new swap.state file without keeping any numbered copies of the previous files.

In summary, squid automatically shuts and restarts the files if log file rotate is configured to 0. This makes it possible for outside logfile security solutions like newsyslog to keep the logs updated.

How Large of a File May Access.Log Potentially Be?

There is no onerous restriction on log data size with Squid. Yet, some programs impose strict limits on the size of individual files. Though, Squid exits with a read failure, if the log file becomes more extensive than the OS allows. Therefore, the log files for Squid must be rotated on a continuous basis to prevent them from becoming too extensive.

Keeping Track of Logs

Surely Access.log, saved in the system’s native format, is the log file of choice for analytical purposes. However, the log file has to be collected on a regular basis to conduct long term analyses. While, Squid provides a simple application programming interface (API) for spinning log files so they are relocated or deleted without affecting active cache activities.

It is suggested that you set up a scheduled task to cycle the system logs each 24, 12, or 8 hours, based upon the amount of disk space available for log storing files. Increase the value of the logfile rotate to a suitable length of time. The log files may be securely transferred to your analytical site in one go during a period of low activity.

In the same fashion, reducing the log data during non peak hours before the transfer is possible. The records are combined into a single file on the analysis server. Thus, the output is a single file for 24 hours. If you activate log icp queries, your daily deflated log data and occupied cache size might approach 1 GB. To estimate your log files’ size, visit the cache manager’s link for more information.

Guidelines for Working with and Analysing Log Files

Firstly, avoid disclosing sensitive customer information while sharing findings. Logs should be kept secret unless they are fully anonymized. There are privacy rules in most nations, while in some, you may only be permitted to maintain specific records for a particular amount of time.

Secondly, the log files should be rotated and processed at least once daily. Otherwise, the log files get very big, if you don’t process them. There, my log files balloon to unmanageable proportions. So, dedicate a huge enough drive to logging if you intend to function the logs.

Thirdly, be mindful of the size while carrying out the processing. Processing log files could end up taking more time than actually creating them.

Fourthly, keep your focus on the figures that matter to you. Data over and above your wildest imagination can be found in your file system, some readily apparent and some only revealed by combining multiple perspectives. A few prominent people to keep an eye on are as follows:

  • These are the hosts that are accessing your cache.
  • Latency is the duration it takes for an HTTP request to complete.
  • In most cases, you want to separate out the timings for strikes, omissions, and totals. The median is favoured above the mean for another reason.

What does ERR_LIFETIME_EXP Mean?

In this situation, this indicates that the data transmission was interrupted due to a delay. It’s possible the user abandoned the session because the entity’s processing was taking too long. However, squid may have kept trying to get the item regardless of the quick abort options. Must be remembered, Squid has a hard limit on how long a socket is open. Therefore the blocked connection was terminated, and an ERR LIFETIME EXP error was recorded.

Thank you for reading Understanding Squid Proxy Logs and How to View Logs. We shall conclude. 

Understanding Squid Proxy Logs and How to View Logs Conclusion

In summary, logging is an integral part of managing a Squid server. It helps us to monitor our system and analyze user activity. The access log provides valuable information, such as the type of requests, latency, and cache hits/misses. Setting up a rotation schedule for log files and following privacy regulations when analysing and sharing findings is vital. Proper file rotation, analysis, and monitoring  helps us to maintain an efficient and secure Squid server.

Do explore more of Squid content by navigating to our blog over here for more

Avatar for Farhan Yousuf
Farhan Yousuf

I am a content writer with more than five years of experience in the field. I have written for a variety of industries, and I am highly interested in learning new things. I have a knack for writing engaging copy that captures the reader's attention. In my spare time, I like to read and travel.

0 0 votes
Article Rating
Notify of
Inline Feedbacks
View all comments
Would love your thoughts, please comment.x