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HotCRP Conference Review Software Build Status

HotCRP is awesome software for managing review processes, especially for academic conferences. It supports paper submission, review and comment management, rebuttals, and the PC meeting. Its main strengths are flexibility and ease of use in the review process, especially through smart paper search and an extensive tagging facility. It has been widely used in computer science conferences and for internal review processes at several large companies.

Multitrack conferences with per-track deadlines should use other software.

HotCRP is the open-source version of the software running on If you want to run HotCRP without setting up your own server, use


HotCRP runs on Unix, including Mac OS X. It requires the following software:

You may need to install additional packages, such as php73, php73-fpm, php73-intl, php73-mysqlnd, zip, poppler-utils, and sendmail or postfix.


  1. Run lib/ to create the database. Use lib/ OPTIONS to pass options to MySQL, such as --user and --password. Many MySQL installations require privilege to create tables, so you may need sudo lib/ OPTIONS. Run lib/ --help for more information. You will need to decide on a name for your database (no spaces allowed).

    The username and password information for the conference database is stored in conf/options.php, which HotCRP marks as world-unreadable. You must ensure that your PHP can read this file.

    If you don’t want to run lib/, you will have to create your own database and user, initialize the database with the contents of src/schema.sql, and create conf/options.php (using etc/distoptions.php as a guide).

  2. Edit conf/options.php, which is annotated to guide you.

  3. Configure your web server to access HotCRP. For Nginx, all accesses under the HotCRP directory should be handled by php-fpm on index.php. For example, this location makes /testconf access a HotCRP installation in /home/kohler/hotcrp (assuming php-fpm is listening on port 9000):

     location /testconf/ {
         fastcgi_split_path_info ^(/testconf)(/.*)$;
         fastcgi_param PATH_INFO $fastcgi_path_info;
         fastcgi_param SCRIPT_FILENAME /home/kohler/hotcrp/index.php;
         include fastcgi_params;

    You may also add location blocks for Nginx to serve static files under images/, scripts/, and stylesheets/ itself.

  4. Update PHP settings.

    The first three settings, upload_max_filesize, post_max_size, and max_input_vars, may be changed system-wide or in HotCRP’s .htaccess and .user.ini files.

  • upload_max_filesize: Set to the largest file upload HotCRP should accept. 15M is a good default.

  • post_max_size: Set to the largest total upload HotCRP should accept. Must be at least as big as upload_max_filesize. 20M is a good default.

  • max_input_vars: Set to the largest number of distinct input variables HotCRP should accept. 4096 is a good default.

    The last setting, session.gc_maxlifetime, must be changed globally. This provides an upper bound on HotCRP session lifetimes (the amount of idle time before a user is logged out automatically). On Unix machines, systemwide PHP settings are often stored in /etc/php.ini. The suggested value for this setting is 86400, e.g., 24 hours:

    session.gc_maxlifetime = 86400

    If you want sessions to expire sooner, we recommend you set session.gc_maxlifetime to 86400 anyway, then edit conf/options.php to set $Opt["sessionLifetime"] to the correct session timeout.

  1. Edit MySQL’s my.cnf (typical locations: /etc/mysql/my.cnf or /etc/mysql/mysql.conf.d/mysqld.cnf) to ensure that MySQL can handle paper-sized objects. It should contain something like this:


    max_allowed_packet must be at least as large as the largest paper you are willing to accept. It defaults to 1M on some systems, which is not nearly large enough. HotCRP will warn you if it is too small. Some MySQL setups, such as on Mac OS X, may not have a my.cnf by default; just create one. If you edit my.cnf, also restart the mysqld server. On Linux try something like sudo /etc/init.d/mysql restart.

  2. Enable a mail transport agent, such as Postfix or Sendmail. You may need help from an administrator to ensure HotCRP can send mail.

  3. Sign in to the site to create an account. The first account created automatically receives system administrator privilege.

You can set up everything else through the web site itself.

  • Configuration notes

    • Uploaded papers and reviews are limited in size by several PHP configuration variables, set by default to 15 megabytes in the HotCRP directory’s .user.ini (or .htaccess if using Apache).

    • HotCRP PHP scripts can take a lot of memory, particularly if they're doing things like generating MIME-encoded mail messages. By default HotCRP sets the PHP memory limit to 128MB.

    • Most HotCRP settings are assigned in the conference database’s Settings table. The Settings table can also override values in conf/options.php: a Settings record with name "opt.XXX" takes precedence over option $Opt["XXX"].

Database access

Run lib/ at the shell prompt to back up the database. This will write the database’s current structure and comments to the standard output. As typically configured, HotCRP stores all paper submissions in the database, so the backup file may be quite large.

Run lib/ BACKUPFILE at the shell prompt to restore the database from a backup stored in BACKUPFILE.

Run lib/ at the shell prompt to get a MySQL command prompt for the conference database.


HotCRP code can be updated at any time without bringing down the site. If you obtained the code from git, use git pull. if you obtained the code from a tarball, copy the new version over your old code, preserving conf/options.php. For instance, using GNU tar:

% tar --strip=1 -xf ~/hotcrp-NEWVERSION.tar.gz


HotCRP is available under the Click license, a BSD-like license. See the LICENSE file for full license terms.


Eddie Kohler, Harvard

  • HotCRP is based on CRP, which was written by Dirk Grunwald, University of Colorado
  • HotCRP’s banal is substantially modified from the original banal by Geoff Voelker, UCSD