# Parrot User's Manual

October 2011

Parrot is Copyright (C) 2003-2004 Douglas Thain and Copyright (C) 2005- The University of Notre Dame. All rights reserved. This software is distributed under the GNU General Public License. See the file COPYING for details.

Please use the following citation to refer to Parrot:

- Douglas Thain and Miron Livny, Parrot: An Application Environment for Data-Intensive Computing, Scalable Computing: Practice and Experience, Volume 6, Number 3, Pages 9--18, 2005.

  ## Overview

  Parrot is a tool for attaching old programs to new storage systems. Parrot makes a remote storage system appear as a file system to a legacy application. Parrot does not require any special privileges, any recompiling, or any change whatsoever to existing programs. It can be used by normal users doing normal tasks. For example, an anonymous FTP service is made available to `vi` like so:

      % parrot_run vi /anonftp/ftp.gnu.org/pub/README

  Parrot is useful to users of distributed systems, because it frees them from rewriting code to work with new systems and relying on remote administrators to trust and install new software. Parrot is also useful to developers of distributed systems, because it allows rapid deployment of new code to real applications and real users that do not have the time, inclination, or permissions to build a kernel-level filesystem.

  Parrot currently supports a variety of remote I/O systems, all detailed below. We welcome contributions of new remote I/O drivers from others. However, if you are working on a protocol driver please drop us a note so that we can make sure work is not duplicated.

  Almost any application - whether static or dynmically linked, standard or commercial, command-line or GUI - should work with Parrot. There are a few exceptions. Because Parrot relies on the Linux `ptrace` interface any program that relies on the ptrace interface cannot run under Parrot. This means Parrot cannot run a debugger, nor can it run itself recursively. In addition, Parrot cannot run setuid programs, as the operating system system considers this a security risk.

  Parrot also provide a new experimental features called identity boxing. This feature allows you to securely run a visiting application within a protection domain without become root or creating a new account. Read below for more information on identity boxing.

  Parrot currently runs on the Linux operating system with either Intel compatible (i386) or AMD compatible (x86_64) processors. It relies on some fairly low level details in order to implement system call trapping. Ports to other platforms and processors Linux may be possible in the future.

  Like any software, Parrot is bound to have some bugs. Please check the known bugs page for the latest scoop.

  ## Installation

  Parrot is distributed as part of the Cooperative Computing Tools. To install, please read the cctools installation instructions.

  ## Examples

  To use Parrot, you simply use the `parrot` command followed by any other Unix program. For example, to run a Parrot-enabled `vi`, execute this command:

      % parrot_run vi /anonftp/ftp.gnu.org/pub/README

  Of course, it can be clumsy to put `parrot_run` before every command you run, so try starting a shell with Parrot already loaded:

      % parrot_run bash

  Now, you should be able to run any standard command using Parrot filenames. Here are some examples to get you thinking:

      % cp /http/www.nd.edu/~dthain/papers/parrot-agm2003.pdf .
      % grep Yahoo /http/www.yahoo.com
      % set autolist
      % cat /anonftp/ftp.gnu.org/pub[Press TAB here]

  Hint: You may find it useful to have some visual indication of when Parrot is active, so we recommend that you modify your shell startup scripts to change the prompt when Parrot is enabled. If you use `tcsh`, you might add something like this to your `.cshrc`:
              if ( $?PARROT_ENABLED ) then
                      set prompt = " (Parrot) %n@%m%~%# "
              else
                      set prompt = " %n@%m%~%# "
              endif

  We have limited the examples so far to HTTP and anonymous FTP, as they are the only services we know that absolutely everyone is familiar with. There are a number of other more powerful and secure remote services that you may be less familiar with. Parrot supports them in the same form: The filename begins with the service type, then the host name, then the file name. Here are all the currently supported services:

  example path | remote service | more info
  /http/www.somewhere.com/index.html | Hypertext Transfer Protocol | included
  /grow/www.somewhere.com/index.html | GROW - Global Read-Only Web Filesystem | included
  /ftp/ftp.cs.wisc.edu/RoadMap | File Transfer Protocol | included
  /anonftp/ftp.cs.wisc.edu/RoadMap | Anonymous File Transfer Protocol | included
  /gsiftp/ftp.globus.org/path | Globus Security + File Transfer Protocol | more info
  /irods/host:port/zone/home/user/path | iRODS | more info
  /hdfs/namenode:port/path | Hadoop Distributed File System (HDFS) | more info
  /xrootd/host:port/path | XRootD/Scalla Distributed Storage System (xrootd) | more info
  /cvmfs/grid.cern.ch/path | CernVM-FS | more info
  /chirp/target.cs.wisc.edu/path | Chirp Storage System | included + more info

  The following protocols have been supported in the past, but are not currently in active use.

  /nest/nest.cs.wisc.edu/path | Network Storage Technology | more info
  /rfio/host.cern.ch/path | Castor Remote File I/O | more info
  /dcap/dcap.cs.wisc.edu/pnfs/cs.wisc.edu/path | DCache Access Protocol | more info
  /lfn/logical/path | Logical File Name - Grid File Access Library | more info
  /srm/server/path | Site File Name - Grid File Access Library | more info
  /guid/abc123 | Globally Unique File Name - Grid File Access Library | more info
  /gfal/protocol://host//path | Grid File Access Library | more info

  You will notice quite quickly that not all remote I/O systems provide all of the functionality common to an ordinary file system. For example, HTTP is incapable of listing files. If you attempt to perform a directory listing on an HTTP server, Parrot will attempt to keep `ls` happy by producing a bogus directory entry:

          % parrot_run ls -la /http/www.yahoo.com/
          -r--r--r--    1 dthain   dthain          0 Jul 16 11:50 /http/www.yahoo.com

  A less-drastic example is found in FTP. If you attempt to perform a directory listing of an FTP server, Parrot fills in the available information -- the file names and their sizes -- but again inserts bogus information to fill the rest out:

          % parrot_run ls -la /anonftp/ftp.gnu.org/pub
          -rwxrwxrwx 1 dthain dip    580 Oct  5 16:00 CRYPTO.README
          -rwxrwxrwx 1 dthain dip 166697 Oct  5 16:00 find.txt.gz
          drwxrwxrwx 1 dthain dip      0 Oct  5 16:00 gnu
      ...

  If you would like to get a better idea of the underlying behavior of Parrot, try running it with the `-d remote` option, which will display all of the remote I/O operations that it performs on a program's behalf:

          % parrot_run -d remote ls -la /anonftp/ftp.gnu.org
          ...
          ftp.cs.wisc.edu <-- TYPE I
          ftp.cs.wisc.edu --> 200 Type set to I.
          ftp.cs.wisc.edu <-- PASV
          ftp.cs.wisc.edu --> 227 Entering Passive Mode (128,105,2,28,194,103)
          ftp.cs.wisc.edu <-- NLST /
          ftp.cs.wisc.edu --> 150 Opening BINARY mode data connection for file list.
          ...

  If your program is upset by the unusual semantics of such storage systems, then consider using the Chirp protocol and server:

  ## The Chirp Protocol and Server

  Although Parrot works with many different protocols, is it limited by the capabilities provided by each underlying system. (For example, HTTP does not have reliable directory listings.) Thus, we have developed a custom protocol, Chirp, which provides secure remote file access with all of the capabilities needed for running arbitrary Unix programs. Chirp is included with the distribution of Parrot, and requires no extra steps to install.

  To start a Chirp server, simply do the following:

          % chirp_server -d all

  The -d all option turns on debugging, which helps you to understand how it works initially. You may remove this option once everything is working.

  Suppose the Chirp server is running on `bird.cs.wisc.edu`. Using Parrot, you may access all of the Unix features of that host from elsewhere:

          % parrot_run tcsh
          % cd /chirp/bird.cs.wisc.edu
          % ls -la
          % ...

  In general, Parrot gives better performance and usability with Chirp than with other protocols. You can read extensively about the Chirp server and protocol in the Chirp manual.

  In addition, Parrot provides several custom command line tools (`parrot_getacl`, `parrot_setacl`, `parrot_lsalloc`, and `parrot_mkalloc`) that can be used to manage the access control and space allocation features of Chirp from the Unix command line.

  ## Name Resolution

  In addition to accessing remote storage, Parrot allows you to create a custom namespace for any program. All file name activity passes through the Parrot name resolver, which can transform any given filename according to a series of rules that you specify.

  The simplest name resolver is the mountlist, given by the -m mountfile option. This file corresponds closely to `/etc/ftsab` in Unix. A mountlist is simply a file with two columns. The first column gives a logical directory or file name, while the second gives the physical path that it must be connected to.

  For example, if a database is stored at an FTP server under the path `/anonftp/ftp.cs.wisc.edu/db`, it may be spliced into the filesystem under `/dbase` with a mount list like this:

           /dbase       /anonftp/ftp.cs.wisc.edu/db

  Instruct Parrot to use the mountlist as follows:

          % parrot_run -m mountfile tcsh
          % cd /dbase
          % ls -la

  A single mount entry may be given on the command line with the -M option as follows:

          % parrot_run -M /dbase=/anonftp/ftp.cs.wisc.edu/db tcsh

  A more sophisticated way to perform name binding is with an external resolver. This is a program executed whenever Parrot needs to locate a file or directory. The program accepts a logical file name and then returns the physical location where it can be found.

  Suppose that you have a database service that locates the nearest copy of a file for you. If you run the command `locate_file`, it will print out the nearest copy of a file. For example:

          % locate_file /1523.data
          /chirp/server.nd.edu/mix/1523.data

  To connect the program `locate_file` to Parrot, simply give a mount string that specifies the program as a resolver:

          % parrot_run -M /dbase=resolver:/path/to/locate_file tcsh

  Now, if you attempt to access files under /dbase, Parrot will execute `locate_file` and access the data stored there:

          % cat /dbase/1523.data
          (see contents of /chirp/server.nd.edu/mix/1523.data)

  ## More Efficient Copies with `parrot_cp`

  If you are using Parrot to copy lots of files across the network, you may see better performance using the `parrot_cp` tool. This program looks like an ordinary `cp`, but it makes use of an optimized Parrot system call that streams entire files over the network, instead of copying them block by block.

  To use `parrot_cp`, simply use your shell to alias calls to `cp` with calls to `parrot_cp`:

      % parrot_run tcsh
      % alias cp parrot_cp
      % cp /tmp/mydata /chirp/server.nd.edu/joe/data
      % cp -rR /chirp/server.nd.edu/joe /tmp/joe

  If run outside of Parrot, `parrot_cp` will operate as an ordinary `cp` without any performance gain or loss.

  ## Notes on Protocols

  ### HTTP Proxy Servers

  HTTP, CVMFS, and GROW can take advantage of standard HTTP proxy servers. To route requests through a single proxy server, set the HTTP_PROXY environment variable to the server name and port:

          % setenv HTTP_PROXY "http://proxy.nd.edu:8080"

  Multiple proxy servers can be given, separated by a semicolon. This will cause Parrot to try each proxy in order until one succeeds. If `DIRECT` is given as the last name in the list, then Parrot will fall back on a direct connection to the target web server. For example:

          % setenv HTTP_PROXY "http://proxy.nd.edu:8080;http://proxy.wisc.edu:1000;DIRECT"

  ### GROW - Global Read Only Web Filesystem

  Although the strict HTTP protocol does not allow for correct structured directory listings, it is possible to emulate directory listings with a little help from the underlying filesystem. We call this technique GROW, a global filesystem based on the Web. GROW requires the exporter of data to run a script (`make_growfs`) that generates a complete directory listing of the data that you wish to export. This directory listing is then used to produce reliable metadata. Of course, if the data changes, the script must be run again, so GROW is only useful for data that changes infrequently.

  To set up an GROW filesystem, you must run `make_growfs` on the web server machine with the name of the local storage directory as the argument. For example, suppose that the web server `my.server.com` stores pages for the URL `http://my.server.com/~fred` in the local directory `/home/fred/www`. In this case, you should run the following command:

          % make_growfs /home/fred/www

  Now, others may perceive the web server as a file server under the /grow hierarchy. For example:

          % parrot_run tcsh
          % cd /grow/my.server.com/~fred
          % ls -la

  In addition to providing precise directory metadata, GROW offers two additional advantages over plain HTTP:
- Aggressive Caching. GROW caches files in an on-disk cache, but unlike plain HTTP, does not need to issue up-to-date checks against the server. Using the cached directory metadata, it can tell if a file is up-to-date without any network communication. The directory is only checked for changes at the beginning of program execution, so changes become visible only to newly executed programs.
- SHA-1 Integrity. `make_growfs` generates SHA-1 checksums on the directory and each file so that the integrity of the system can be verified at runtime. If a checksum fails, GROW will attempt to reload the file or directory listing in order to repair the error, trying until the master timeout (set by the -T option) expires. This will also occur if the underlying files have been modified and `make_growfs` has not yet been re-run. If necessary, checksums can be disabled by giving the `-k` option to either Parrot or `make_growfs`.

  ### CVMFS - CernVM-FS

  CVMFS is a read-only filesystem, which was initially based on GROW. It is used within CernVM-FS to provide access to software repositories. It may be used outside of CernVM-FS by mounting it as a FUSE module. Parrot makes it possible to access CVMFS in cases where mounting CVMFS via FUSE is not an option. Like GROW, CVMFS makes use of web proxies and local disk caching for scalability. For security, data integrity is verified with cryptographic checksums. For increased reliability and performance, CVMFS repositories may also be mirrored in multiple locations and accessed via groups of load-balanced web proxies, with fail-over between groups.

  The CVMFS repositories hosted by the CernVM project are enabled by default. To access a different repository, it is necessary to configure parrot to know how to access the repository. This may be done with the `-r` option or with the `PARROT_CVMFS_REPO` environment variable. The repository configuration syntax is

      repo_name:options  repo_name2:option2  ...

  The repository with `repo_name` is used when the parrot user attempts to access the matching path `/cvmfs/repo_name/...`. The configured repository name may begin with `*`, which acts as a wildcard, matching one or more characters in the requested repository name. This is useful when multiple repositories are hosted at the same site and all configuration details are the same except the beginnings of the repository names, as in `atlas.cern.ch` and `cms.cern.ch`. Any `*` appearing in the options is replaced by the characters in the requested path that were matched by the `*` in the configured repository name. If a cvmfs path matches more than one configured repository, the last one appearing in the configuration takes precedence.

  The format of the repository options is

      option1=value1,option2=value2,...

  Literal spaces, tabs, newlines, asterisks, equal signs, or commas in the options must be proceeded by a backslash to avoid being interpreted as delimiters. If the same option is specified more than once, the last value takes precedence. The possible options are listed in the table below. The `url` option is required and has no default. The `proxies` option is required and defaults to the proxy used by parrot, if any.

  url=URL | The URL of the CernVM-FS server(s): 'url1;url2;...'
  proxies=HTTP_PROXIES | Set the HTTP proxy list, such as 'proxy1|proxy2'; default is given by -P option (HTTP_PROXY)
  | Proxies separated by '|' are randomly chosen for load balancing. Groups of proxies separated by ';' may be specified for failover. If the first group fails, the second group is used, and so on down the chain.
  cachedir=DIR | Where to store disk cache; default is within parrot temp directory (-t option)
  timeout=SECONDS | Timeout for network operations; default is given by -T option (PARROT_TIMEOUT)
  timeout_direct=SECONDS | Timeout in for network operations without proxy; default is given by -T option (PARROT_TIMEOUT)
  max_ttl=MINUTES | Maximum TTL for file catalogs; default: take from catalog
  allow_unsigned | Accept unsigned catalogs (allows man-in-the-middle attacks)
  whitelist=URL | HTTP location of trusted catalog certificates (defaults is /.cvmfswhitelist)
  pubkey=PEMFILE | Public RSA key that is used to verify the whitelist signature.
  rebuild_cachedb | Force rebuilding the quota cache db from cache directory
  quota_limit=MB | Limit size of cache. -1 (the default) means unlimited.
  | If not -1, files larger than quota_limit-quota_threshold will not be readable.
  quota_threshold=MB | Cleanup cache until size is <= threshold
  deep_mount=prefix | Path prefix if a repository is mounted on a nested catalog
  repo_name=NAME | Unique name of the mounted repository; default is the name used for this configuration entry
  mountpoint=PATH | Path to root of repository; default is /cvmfs/repo_name
  blacklist=FILE | Local blacklist for invalid certificates. Has precedence over the whitelist.

  Setting the CVMFS configuration overrides the default configuration. If it is desired to configure additional repositories but still retain the default repositories, the configuration entry `<default-repositories>` may be put in the configuration string. Example:

      parrot_run -r '<default-repositories> my.repo:url=http://cvmfs.server.edu/cvmfs/my.repo.edu' ...

  The configuration of the default repositories may be modified by specifying additional options using the syntax `<default-repositories>:option1=value1,option2=value2`.

  The CVMFS library can only support one active repository open at a time. If a program attempts to access more than one repository in a session, Parrot will emit an error. If the optional argument --cvmfs-repo-switching is given to `parrot_run`, then Parrot will switch repositories at run-time by re-initializing the CVMFS library. This feature is experimental.

  ### Hadoop Distributed File System (HDFS)

  HDFS is the primary distributed filesystem used in the Hadoop project. Parrot supports read and write access to HDFS systems using the `parrot_run_hdfs` wrapper. This script checks that the appropriate environmental variables are defined and calls `parrot`.

  In particular, you must ensure that you define the following environmental variables:

      JAVA_HOME     Location of your Java installation.
      HADOOP_HOME   Location of your Hadoop installation.

  Based on these environmental variables, `parrot_run_hdfs` will attempt to find the appropriate paths for `libjvm.so` and `libhdfs.so`. These paths are stored in the environmental variables `LIBJVM_PATH` and `LIBHDFS_PATH`, which are used by the HDFS Parrot module to load the necessary shared libraries at run-time. To avoid the startup overhead of searching for these libraries, you may set the paths manually in your environment before calling `parrot_run_hdfs`, or you may edit the script directly.

  Note that while Parrot supports read access to HDFS, it only provides write-once support on HDFS. This is because the current implementations of HDFS do not provide reliable append operations. Likewise, files can only be opened in either read (`O_RDONLY`) or write mode (`O_WRONLY`), and not both (`O_RDWR`).

  ## Identity Boxing

  Parot provides a unique feature known as identity boxing. This feature allows you to run a (possibly) untrusted program within a protection domain, as if it were run in a completely separate account. Using an identity box, you do not need to become root or even to manage account names: you can create any identity that you like on the fly.

  For example, suppose that you wish to allow a friend to log into your private workstation. Instead of creating a new account, simply use a script supplied with Parrot to create an identity box:

      % whoami
      dthain
      % parrot_identity_box MyFriend
      % whoami
      MyFriend
      % touch ~dthain/private-data
      touch: creating ~dthain/private-data': Permission denied

  Note that the shell running within the identity box cannot change or modify any of the supervising user's data. In fact, the contained user can only access items that are world-readable or world-writable.

  You can give the contained user access to other parts of the filesystem by creating access control lists. (ACLs) An ACL is a list of users and the resources that they are allowed to access. Each directory has it's own ACL in the file `.__acl`. This file does not appear in a directory listing, but you can read and write it just the same.

  For example, `MyFriend` above can see his initial ACL as follows:

      % cat .__acl
      MyFriend rwlxa

  This means that `MyFriend` can read, write, list, execute, and administer items in the current directory. Now, suppose that `MyFriend` wants to allow `Freddy` read access to the same directory. Simply edit the ACL file to read:

      MyFriend rwlxa
      Freddy   rl

  Identity boxing and ACLs are particularly useful when using distributed storage. You can read more about ACLs and identity boxing in the Chirp manual.

  ## 64-Bit Support

  In all modes, Parrot supports applications that access large (>2GB) files that require 64-bit seek pointers. However, we have found that many tools and filesystems do not manipulate such large files properly. If possible, we advise users to break up files into smaller pieces for processing.

  Parrot supports 64 bit programs and processors in the following combinations:

  Program Type
  32-bit | 64-bit | CPU Type
  YES | NO | Parrot for 32-bit X86 CPU Pentium, Xeon, Athlon, Sempron
  YES | YES | Parrot for 64-bit X86_64 CPU Opteron, Athlon64, Turion64, Sempron64

  ## For More Information

  For the latest information on Parrot, visit the home page:
- Parrot Home Page An exhaustive list of all options and commands can be found in the manual pages:
- parrot_run
- parrot_run_hdfs
- parrot_cp
- parrot_md5
- parrot_getacl
- parrot_setacl
- parrot_mkalloc
- parrot_lsalloc
- parrot_locate
- parrot_timeout
- parrot_whoami