This is a list of common pitfalls on using Composer, and how to avoid them.


  1. When facing any kind of problems using Composer, be sure to work with the latest version. See self-update for details.

  2. Before asking anyone, run composer diagnose to check for common problems. If it all checks out, proceed to the next steps.

  3. Make sure you have no problems with your setup by running the installer's checks via curl -sS | php -- --check.

  4. Try clearing Composer's cache by running composer clear-cache.

  5. Ensure you're installing vendors straight from your composer.json via rm -rf vendor && composer update -v when troubleshooting, excluding any possible interferences with existing vendor installations or composer.lock entries.

Package not found#

  1. Double-check you don't have typos in your composer.json or repository branches and tag names.

  2. Be sure to set the right minimum-stability. To get started or be sure this is no issue, set minimum-stability to "dev".

  3. Packages not coming from Packagist should always be defined in the root package (the package depending on all vendors).

  4. Use the same vendor and package name throughout all branches and tags of your repository, especially when maintaining a third party fork and using replace.

  5. If you are updating to a recently published version of a package, be aware that Packagist has a delay of up to 1 minute before new packages are visible to Composer.

  6. If you are updating a single package, it may depend on newer versions itself. In this case add the --with-dependencies argument or add all dependencies which need an update to the command.

Package is not updating to the expected version#

Try running php composer.phar why-not [package-name] [expected-version].

Dependencies on the root package#

When your root package depends on a package which ends up depending (directly or indirectly) back on the root package itself, issues can occur in two cases:

  1. During development, if you are on a branch like dev-main and the branch has no branch-alias defined, and the dependency on the root package requires version ^2.0 for example, the dev-main version will not satisfy it. The best solution here is to make sure you first define a branch alias.

  2. In CI (Continuous Integration) runs, the problem might be that Composer is not able to detect the version of the root package properly. If it is a git clone it is generally alright and Composer will detect the version of the current branch, but some CIs do shallow clones so that process can fail when testing pull requests and feature branches. In these cases the branch alias may then not be recognized. The best solution is to define the version you are on via an environment variable called COMPOSER_ROOT_VERSION. You set it to dev-main for example to define the root package's version as dev-main. Use for example: COMPOSER_ROOT_VERSION=dev-main composer install to export the variable only for the call to composer, or you can define it globally in the CI env vars.

Root package version detection#

Composer relies on knowing the version of the root package to resolve dependencies effectively. The version of the root package is determined using a hierarchical approach:

  1. composer.json Version Field: Firstly, Composer looks for a version field in the project's root composer.json file. If present, this field specifies the version of the root package directly. This is generally not recommended as it needs to be constantly updated, but it is an option.

  2. Environment Variable: Composer then checks for the COMPOSER_ROOT_VERSION environment variable. This variable can be explicitly set by the user to define the version of the root package, providing a straightforward way to inform Composer of the exact version, especially in CI/CD environments or when the VCS method is not applicable.

  3. Version Control System (VCS) Inspection: Composer then attempts to guess the version by interfacing with the version control system of the project. For instance, in projects versioned with Git, Composer executes specific Git commands to deduce the project's current version based on tags, branches, and commit history. If a .git directory is missing or the history is incomplete because CI is using a shallow clone for example, this detection may fail to find the correct version.

  4. Fallback: If all else fails, Composer uses 1.0.0 as default version.

Note that relying on the default/fallback version might potentially lead to dependency resolution issues, especially when the root package depends on a package which ends up depending (directly or indirectly) back on the root package itself.

Network timeout issues, curl error#

If you see something along the lines of:

Failed to download * curl error 28 while downloading * Operation timed out after 300000 milliseconds

It means your network is probably so slow that a request took over 300seconds to complete. This is the minimum timeout Composer will use, but you can increase it by increasing the default_socket_timeout value in your php.ini to something higher.

Package not found in a Jenkins-build#

  1. Check the "Package not found" item above.

  2. The git-clone / checkout within Jenkins leaves the branch in a "detached HEAD"-state. As a result, Composer may not able to identify the version of the current checked out branch and may not be able to resolve a dependency on the root package. To solve this problem, you can use the "Additional Behaviours" -> "Check out to specific local branch" in your Git-settings for your Jenkins-job, where your "local branch" shall be the same branch as you are checking out. Using this, the checkout will not be in detached state any more and the dependency on the root package should become satisfied.

I have a dependency which contains a "repositories" definition in its composer.json, but it seems to be ignored.#

The repositories configuration property is defined as root-only. It is not inherited. You can read more about the reasons behind this in the "why can't Composer load repositories recursively?" article. The simplest work-around to this limitation, is moving or duplicating the repositories definition into your root composer.json.

I have locked a dependency to a specific commit but get unexpected results.#

While Composer supports locking dependencies to a specific commit using the #commit-ref syntax, there are certain caveats that one should take into account. The most important one is documented, but frequently overlooked:

Note: While this is convenient at times, it should not be how you use packages in the long term because it comes with a technical limitation. The composer.json metadata will still be read from the branch name you specify before the hash. Because of that in some cases it will not be a practical workaround, and you should always try to switch to tagged releases as soon as you can.

There is no simple work-around to this limitation. It is therefore strongly recommended that you do not use it.

Need to override a package version#

Let's say your project depends on package A, which in turn depends on a specific version of package B (say 0.1). But you need a different version of said package B (say 0.11).

You can fix this by aliasing version 0.11 to 0.1:


    "require": {
        "A": "0.2",
        "B": "0.11 as 0.1"

See aliases for more information.

Figuring out where a config value came from#

Use php composer.phar config --list --source to see where each config value originated from.

Memory limit errors#

The first thing to do is to make sure you are running Composer 2, and if possible 2.2.0 or above.

Composer 1 used much more memory and upgrading to the latest version will give you much better and faster results.

Composer may sometimes fail on some commands with this message:

PHP Fatal error: Allowed memory size of XXXXXX bytes exhausted <...>

In this case, the PHP memory_limit should be increased.

Note: Composer internally increases the memory_limit to 1.5G.

To get the current memory_limit value, run:

php -r "echo ini_get('memory_limit').PHP_EOL;"

Try increasing the limit in your php.ini file (ex. /etc/php5/cli/php.ini for Debian-like systems):

; Use -1 for unlimited or define an explicit value like 2G
memory_limit = -1

Composer also respects a memory limit defined by the COMPOSER_MEMORY_LIMIT environment variable:

COMPOSER_MEMORY_LIMIT=-1 composer.phar <...>

Or, you can increase the limit with a command-line argument:

php -d memory_limit=-1 composer.phar <...>

However, please note that setting the memory limit using these methods primarily addresses memory issues within Composer itself and its immediate processes. Child processes or external commands invoked by Composer may still require separate adjustments if they have their own memory requirements.

This issue can also happen on cPanel instances, when the shell fork bomb protection is activated. For more information, see the documentation of the fork bomb feature on the cPanel site.

Xdebug impact on Composer#

To improve performance when the Xdebug extension is enabled, Composer automatically restarts PHP without it. You can override this behavior by using an environment variable: COMPOSER_ALLOW_XDEBUG=1.

Composer will always show a warning if Xdebug is being used, but you can override this with an environment variable: COMPOSER_DISABLE_XDEBUG_WARN=1. If you see this warning unexpectedly, then the restart process has failed: please report this issue.

"The system cannot find the path specified" (Windows)#

  1. Open regedit.
  2. Search for an AutoRun key inside HKEY_LOCAL_MACHINE\Software\Microsoft\Command Processor, HKEY_CURRENT_USER\Software\Microsoft\Command Processor or HKEY_LOCAL_MACHINE\Software\Wow6432Node\Microsoft\Command Processor.
  3. Check if it contains any path to a non-existent file, if it's the case, remove them.

API rate limit and OAuth tokens#

Because of GitHub's rate limits on their API it can happen that Composer prompts for authentication asking your username and password so it can go ahead with its work.

If you would prefer not to provide your GitHub credentials to Composer you can manually create a token using the procedure documented here.

Now Composer should install/update without asking for authentication.

proc_open(): fork failed errors#

If Composer shows proc_open() fork failed on some commands:

PHP Fatal error: Uncaught exception 'ErrorException' with message 'proc_open(): fork failed - Cannot allocate memory' in phar

This could be happening because the VPS runs out of memory and has no Swap space enabled.

free -m
total used free shared buffers cached
Mem: 2048 357 1690 0 0 237
-/+ buffers/cache: 119 1928
Swap: 0 0 0

To enable the swap you can use for example:

/bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=1024
/sbin/mkswap /var/swap.1
/bin/chmod 0600 /var/swap.1
/sbin/swapon /var/swap.1

You can make a permanent swap file following this tutorial.

proc_open(): failed to open stream errors (Windows)#

If Composer shows proc_open(NUL) errors on Windows:

proc_open(NUL): failed to open stream: No such file or directory

This could be happening because you are working in a OneDrive directory and using a version of PHP that does not support the file system semantics of this service. The issue was fixed in PHP 7.2.23 and 7.3.10.

Alternatively it could be because the Windows Null Service is not enabled. For more information, see this issue.

Degraded Mode#

Due to some intermittent issues on Travis and other systems, we introduced a degraded network mode which helps Composer finish successfully but disables a few optimizations. This is enabled automatically when an issue is first detected. If you see this issue sporadically you probably don't have to worry (a slow or overloaded network can also cause those time outs), but if it appears repeatedly you might want to look at the options below to identify and resolve it.

If you have been pointed to this page, you want to check a few things:

  • If you are using ESET antivirus, go in "Advanced Settings" and disable "HTTP-scanner" under "web access protection"
  • If you are using IPv6, try disabling it. If that solves your issues, get in touch with your ISP or server host, the problem is not at the Packagist level but in the routing rules between you and Packagist (i.e. the internet at large). The best way to get these fixed is to raise awareness to the network engineers that have the power to fix it. Take a look at the next section for IPv6 workarounds.
  • If none of the above helped, please report the error.

Operation timed out (IPv6 issues)#

You may run into errors if IPv6 is not configured correctly. A common error is:

The "" file could not be downloaded: failed to
open stream: Operation timed out

We recommend you fix your IPv6 setup. If that is not possible, you can try the following workarounds:

Generic Workaround:

Set the COMPOSER_IPRESOLVE=4 environment variable which will force curl to resolve domains using IPv4. This only works when the curl extension is used for downloads.

Workaround Linux:

On linux, it seems that running this command helps to make ipv4 traffic have a higher priority than ipv6, which is a better alternative than disabling ipv6 entirely:

sudo sh -c "echo 'precedence ::ffff:0:0/96 100' >> /etc/gai.conf"

Workaround Windows:

On windows the only way is to disable ipv6 entirely I am afraid (either in windows or in your home router).

Workaround Mac OS X:

Get name of your network device:

networksetup -listallnetworkservices

Disable IPv6 on that device (in this case "Wi-Fi"):

networksetup -setv6off Wi-Fi

Run Composer ...

You can enable IPv6 again with:

networksetup -setv6automatic Wi-Fi

That said, if this fixes your problem, please talk to your ISP about it to try to resolve the routing errors. That's the best way to get things resolved for everyone.

Composer hangs with SSH ControlMaster#

When you try to install packages from a Git repository and you use the ControlMaster setting for your SSH connection, Composer might hang endlessly and you see a sh process in the defunct state in your process list.

The reason for this is a SSH Bug:

As a workaround, open a SSH connection to your Git host before running Composer:

ssh -t git@mygitserver.tld
php composer.phar update

See also for more information.

Zip archives are not unpacked correctly.#

Composer can unpack zipballs using either a system-provided unzip or 7z (7-Zip) utility, or PHP's native ZipArchive class. On OSes where ZIP files can contain permissions and symlinks, we recommend installing unzip or 7z as these features are not supported by ZipArchive.

Disabling the pool optimizer#

In Composer, the Pool class contains all the packages that are relevant for the dependency resolving process. That is what is used to generate all the rules which are then passed on to the dependency solver. In order to improve performance, Composer tries to optimize this Pool by removing useless package information early on.

If all goes well, you should never notice any issues with it but in case you run into an unexpected result such as an unresolvable set of dependencies or conflicts where you think Composer is wrong, you might want to disable the optimizer by using the environment variable COMPOSER_POOL_OPTIMIZER and run the update again like so:

COMPOSER_POOL_OPTIMIZER=0 php composer.phar update

Now double check if the result is still the same. It will take significantly longer and use a lot more memory to run the dependency resolving process.

If the result is different, you likely hit a problem in the pool optimizer. Please report this issue so it can be fixed.

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