diff --git a/Makefile.am b/Makefile.am
index 7fd29b90a8..c7171d8f5d 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -201,6 +201,7 @@ MODULES =					\
   guix/scripts/hash.scm				\
   guix/scripts/pack.scm				\
   guix/scripts/pull.scm				\
+  guix/scripts/processes.scm			\
   guix/scripts/substitute.scm			\
   guix/scripts/authenticate.scm			\
   guix/scripts/refresh.scm			\
@@ -343,6 +344,7 @@ SCM_TESTS =					\
   tests/ui.scm					\
   tests/status.scm				\
   tests/records.scm				\
+  tests/processes.scm				\
   tests/upstream.scm				\
   tests/combinators.scm				\
   tests/discovery.scm				\
diff --git a/doc/guix.texi b/doc/guix.texi
index 12346c4b8e..214e65a07e 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -193,6 +193,7 @@ Utilities
 * Invoking guix copy::          Copying to and from a remote store.
 * Invoking guix container::     Process isolation.
 * Invoking guix weather::       Assessing substitute availability.
+* Invoking guix processes::     Listing client processes.
 
 Invoking @command{guix build}
 
@@ -6051,6 +6052,7 @@ the Scheme programming interface of Guix in a convenient way.
 * Invoking guix copy::          Copying to and from a remote store.
 * Invoking guix container::     Process isolation.
 * Invoking guix weather::       Assessing substitute availability.
+* Invoking guix processes::     Listing client processes.
 @end menu
 
 @node Invoking guix build
@@ -8751,6 +8753,60 @@ with the @code{-m} option of @command{guix package} (@pxref{Invoking
 guix package}).
 @end table
 
+@node Invoking guix processes
+@section Invoking @command{guix processes}
+
+The @command{guix processes} command can be useful to developers and system
+administrators, especially on multi-user machines and on build farms: it lists
+the current Guix sessions (connections to the daemon), as well as information
+about the processes involved.  Here's an example of the information it
+returns:
+
+@example
+$ sudo guix processes
+SessionPID: 19002
+ClientPID: 19090
+ClientCommand: guix environment --ad-hoc python
+
+SessionPID: 19402
+ClientPID: 19367
+ClientCommand: guix publish -u guix-publish -p 3000 -C 9 @dots{}
+
+SessionPID: 19444
+ClientPID: 19419
+ClientCommand: cuirass --cache-directory /var/cache/cuirass @dots{}
+LockHeld: /gnu/store/@dots{}-perl-ipc-cmd-0.96.lock
+LockHeld: /gnu/store/@dots{}-python-six-bootstrap-1.11.0.lock
+LockHeld: /gnu/store/@dots{}-libjpeg-turbo-2.0.0.lock
+ChildProcess: 20495: guix offload x86_64-linux 7200 1 28800
+ChildProcess: 27733: guix offload x86_64-linux 7200 1 28800
+ChildProcess: 27793: guix offload x86_64-linux 7200 1 28800
+@end example
+
+In this example we see that @command{guix-daemon} has three clients:
+@command{guix environment}, @command{guix publish}, and the Cuirass continuous
+integration tool; their process identifier (PID) is given by the
+@code{ClientPID} field.  The @code{SessionPID} field gives the PID of the
+@command{guix-daemon} sub-process of this particular session.
+
+The @code{LockHeld} fields show which store items are currently locked by this
+session, which corresponds to store items being built or substituted (the
+@code{LockHeld} field is not displayed when @command{guix processes} is not
+running as root.)  Last, by looking at the @code{ChildProcess} field, we
+understand that these three builds are being offloaded (@pxref{Daemon Offload
+Setup}).
+
+The output is in Recutils format so we can use the handy @command{recsel}
+command to select sessions of interest (@pxref{Selection Expressions,,,
+recutils, GNU recutils manual}).  As an example, the command shows the command
+line and PID of the client that triggered the build of a Perl package:
+
+@example
+$ sudo guix processes | \
+    recsel -p ClientPID,ClientCommand -e 'LockHeld ~ "perl"'
+ClientPID: 19419
+ClientCommand: cuirass --cache-directory /var/cache/cuirass @dots{}
+@end example
 
 @c *********************************************************************
 @node GNU Distribution
diff --git a/guix/scripts/processes.scm b/guix/scripts/processes.scm
new file mode 100644
index 0000000000..6a2f603599
--- /dev/null
+++ b/guix/scripts/processes.scm
@@ -0,0 +1,223 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix scripts processes)
+  #:use-module ((guix store) #:select (%store-prefix))
+  #:use-module (guix scripts)
+  #:use-module (guix ui)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-9)
+  #:use-module (srfi srfi-9 gnu)
+  #:use-module (srfi srfi-37)
+  #:use-module (ice-9 ftw)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 rdelim)
+  #:use-module (ice-9 format)
+  #:export (process?
+            process-id
+            process-parent-id
+            process-command
+            processes
+
+            daemon-session?
+            daemon-session-process
+            daemon-session-client
+            daemon-session-children
+            daemon-session-locks-held
+            daemon-sessions
+
+            guix-processes))
+
+;; Process as can be found in /proc on GNU/Linux.
+(define-record-type <process>
+  (process id parent command)
+  process?
+  (id       process-id)                           ;integer
+  (parent   process-parent-id)                    ;integer | #f
+  (command  process-command))                     ;list of strings
+
+(define (write-process process port)
+  (format port "#<process ~a>" (process-id process)))
+
+(set-record-type-printer! <process> write-process)
+
+(define (read-status-ppid port)
+  "Read the PPID from PORT, an input port on a /proc/PID/status file.  Return
+#f for PID 1 and kernel pseudo-processes."
+  (let loop ()
+    (match (read-line port)
+      ((? eof-object?) #f)
+      (line
+       (if (string-prefix? "PPid:" line)
+           (string->number (string-trim-both (string-drop line 5)))
+           (loop))))))
+
+(define %not-nul
+  (char-set-complement (char-set #\nul)))
+
+(define (read-command-line port)
+  "Read the zero-split command line from PORT, a /proc/PID/cmdline file, and
+return it as a list."
+  (string-tokenize (read-string port) %not-nul))
+
+(define (processes)
+  "Return a list of process records representing the currently alive
+processes."
+  ;; This assumes a Linux-compatible /proc file system.  There exists one for
+  ;; GNU/Hurd.
+  (filter-map (lambda (pid)
+                ;; There's a TOCTTOU race here.  If we get ENOENT, simply
+                ;; ignore PID.
+                (catch 'system-error
+                  (lambda ()
+                    (define ppid
+                      (call-with-input-file (string-append "/proc/" pid "/status")
+                        read-status-ppid))
+                    (define command
+                      (call-with-input-file (string-append "/proc/" pid "/cmdline")
+                        read-command-line))
+                    (process (string->number pid) ppid command))
+                  (lambda args
+                    (if (= ENOENT (system-error-errno args))
+                        #f
+                        (apply throw args)))))
+              (scandir "/proc" string->number)))
+
+(define (process-open-files process)
+  "Return the list of files currently open by PROCESS."
+  (let ((directory (string-append "/proc/"
+                                  (number->string (process-id process))
+                                  "/fd")))
+    (map (lambda (fd)
+           (readlink (string-append directory "/" fd)))
+         (or (scandir directory string->number) '()))))
+
+;; Daemon session.
+(define-record-type <daemon-session>
+  (daemon-session process client children locks)
+  daemon-session?
+  (process    daemon-session-process)             ;<process>
+  (client     daemon-session-client)              ;<process>
+  (children   daemon-session-children)            ;list of <process>
+  (locks      daemon-session-locks-held))         ;list of strings
+
+(define (daemon-sessions)
+  "Return two values: the list of <daemon-session> denoting the currently
+active sessions, and the master 'guix-daemon' process."
+  (define (lock-file? file)
+    (and (string-prefix? (%store-prefix) file)
+         (string-suffix? ".lock" file)))
+
+  (let* ((processes (processes))
+         (daemons   (filter (lambda (process)
+                              (match (process-command process)
+                                ((argv0 _ ...)
+                                 (string=? (basename argv0) "guix-daemon"))
+                                (_ #f)))
+                            processes))
+         (children  (filter (lambda (process)
+                              (match (process-command process)
+                                ((argv0 (= string->number argv1) _ ...)
+                                 (integer? argv1))
+                                (_ #f)))
+                            daemons))
+         (master    (remove (lambda (process)
+                              (memq process children))
+                            daemons)))
+    (define (lookup-process pid)
+      (find (lambda (process)
+              (and (process-id process)
+                   (= pid (process-id process))))
+            processes))
+
+    (define (lookup-children pid)
+      (filter (lambda (process)
+                (and (process-parent-id process)
+                     (= pid (process-parent-id process))))
+              processes))
+
+    (values (map (lambda (process)
+                   (match (process-command process)
+                     ((argv0 (= string->number client) _ ...)
+                      (let ((files (process-open-files process)))
+                        (daemon-session process
+                                        (lookup-process client)
+                                        (lookup-children (process-id process))
+                                        (filter lock-file? files))))))
+                 children)
+            master)))
+
+(define (daemon-session->recutils session port)
+  "Display SESSION information in recutils format on PORT."
+  (format port "SessionPID: ~a~%"
+          (process-id (daemon-session-process session)))
+  (format port "ClientPID: ~a~%"
+          (process-id (daemon-session-client session)))
+  (format port "ClientCommand:~{ ~a~}~%"
+          (process-command (daemon-session-client session)))
+  (for-each (lambda (lock)
+              (format port "LockHeld: ~a~%" lock))
+            (daemon-session-locks-held session))
+  (for-each (lambda (process)
+              (format port "ChildProcess: ~a:~{ ~a~}~%"
+                      (process-id process)
+                      (process-command process)))
+            (daemon-session-children session)))
+
+
+;;;
+;;; Options.
+;;;
+
+(define %options
+  (list (option '(#\h "help") #f #f
+                (lambda args
+                  (show-help)
+                  (exit 0)))
+        (option '(#\V "version") #f #f
+                (lambda args
+                  (show-version-and-exit "guix processes")))))
+
+(define (show-help)
+  (display (G_ "Usage: guix processes
+List the current Guix sessions and their processes."))
+  (newline)
+  (display (G_ "
+  -h, --help             display this help and exit"))
+  (display (G_ "
+  -V, --version          display version information and exit"))
+  (newline)
+  (show-bug-report-information))
+
+
+;;;
+;;; Entry point.
+;;;
+
+(define (guix-processes . args)
+  (define options
+    (args-fold* args %options
+                (lambda (opt name arg result)
+                  (leave (G_ "~A: unrecognized option~%") name))
+                cons
+                '()))
+
+  (for-each (lambda (session)
+              (daemon-session->recutils session (current-output-port))
+              (newline))
+            (daemon-sessions)))
diff --git a/po/guix/POTFILES.in b/po/guix/POTFILES.in
index 2e37a19407..74c223b283 100644
--- a/po/guix/POTFILES.in
+++ b/po/guix/POTFILES.in
@@ -32,6 +32,7 @@ guix/scripts/copy.scm
 guix/scripts/pack.scm
 guix/scripts/weather.scm
 guix/scripts/describe.scm
+guix/scripts/processes.scm
 guix/gnu-maintenance.scm
 guix/scripts/container.scm
 guix/scripts/container/exec.scm
diff --git a/tests/processes.scm b/tests/processes.scm
new file mode 100644
index 0000000000..40454bcbc7
--- /dev/null
+++ b/tests/processes.scm
@@ -0,0 +1,86 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (test-processes)
+  #:use-module (guix scripts processes)
+  #:use-module (guix store)
+  #:use-module (guix derivations)
+  #:use-module (guix packages)
+  #:use-module (guix gexp)
+  #:use-module ((guix utils) #:select (call-with-temporary-directory))
+  #:use-module (gnu packages bootstrap)
+  #:use-module (guix tests)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-64)
+  #:use-module (rnrs bytevectors)
+  #:use-module (rnrs io ports)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 threads))
+
+(test-begin "processes")
+
+(test-assert "not a client"
+  (not (find (lambda (session)
+               (= (getpid)
+                  (process-id (daemon-session-client session))))
+             (daemon-sessions))))
+
+(test-assert "client"
+  (with-store store
+    (let* ((session (find (lambda (session)
+                            (= (getpid)
+                               (process-id (daemon-session-client session))))
+                          (daemon-sessions)))
+           (daemon  (daemon-session-process session)))
+      (and (kill (process-id daemon) 0)
+           (string-suffix? "guix-daemon" (first (process-command daemon)))))))
+
+(test-assert "client + lock"
+  (with-store store
+    (call-with-temporary-directory
+     (lambda (directory)
+       (let* ((token1  (string-append directory "/token1"))
+              (token2  (string-append directory "/token2"))
+              (exp     #~(begin #$(random-text)
+                                (mkdir #$token1)
+                                (let loop ()
+                                  (unless (file-exists? #$token2)
+                                    (sleep 1)
+                                    (loop)))
+                                (mkdir #$output)))
+              (guile   (package-derivation store %bootstrap-guile))
+              (drv     (run-with-store store
+                         (gexp->derivation "foo" exp
+                                           #:guile-for-build guile)))
+              (thread  (call-with-new-thread
+                        (lambda ()
+                          (build-derivations store (list drv)))))
+              (_       (let loop ()
+                         (unless (file-exists? token1)
+                           (usleep 200)
+                           (loop))))
+              (session (find (lambda (session)
+                               (= (getpid)
+                                  (process-id (daemon-session-client session))))
+                             (daemon-sessions)))
+              (locks   (daemon-session-locks-held (pk 'session session))))
+         (call-with-output-file token2 (const #t))
+         (equal? (list (string-append (derivation->output-path drv) ".lock"))
+                 locks))))))
+
+(test-end "processes")
