20 files changed, 567 insertions, 317 deletions

diff --git a/doc/manual/expressions/builtins.xml b/doc/manual/expressions/builtins.xml
index ac8ecedd0b1f..615314880aba 100644
--- a/doc/manual/expressions/builtins.xml
+++ b/doc/manual/expressions/builtins.xml
@@ -210,42 +210,6 @@ if builtins ? getEnv then builtins.getEnv "PATH" else ""</programlisting>
 
   </varlistentry>
 
-  <varlistentry><term><function>builtins.match</function>
-  <replaceable>regex</replaceable> <replaceable>str</replaceable></term>
-
-  <listitem><para>Returns a list if the <link
-  xlink:href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04">extended
-  POSIX regular expression</link> <replaceable>regex</replaceable>
-  matches <replaceable>str</replaceable> precisely, otherwise returns
-  <literal>null</literal>.  Each item in the list is a regex group.
-
-<programlisting>
-builtins.match "ab" "abc"
-</programlisting>
-
-Evaluates to <literal>null</literal>.
-
-<programlisting>
-builtins.match "abc" "abc"
-</programlisting>
-
-Evaluates to <literal>[ ]</literal>.
-
-<programlisting>
-builtins.match "a(b)(c)" "abc"
-</programlisting>
-
-Evaluates to <literal>[ "b" "c" ]</literal>.
-
-<programlisting>
-builtins.match "[[:space:]]+([[:upper:]]+)[[:space:]]+" "  FOO   "
-</programlisting>
-
-Evaluates to <literal>[ "foo" ]</literal>.
-
-  </para></listitem>
-  </varlistentry>
-
   <varlistentry><term><function>builtins.elem</function>
   <replaceable>x</replaceable> <replaceable>xs</replaceable></term>
 
@@ -726,6 +690,42 @@ map (x: "foo" + x) [ "bar" "bla" "abc" ]</programlisting>
   </varlistentry>
 
 
+  <varlistentry><term><function>builtins.match</function>
+  <replaceable>regex</replaceable> <replaceable>str</replaceable></term>
+
+  <listitem><para>Returns a list if the <link
+  xlink:href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04">extended
+  POSIX regular expression</link> <replaceable>regex</replaceable>
+  matches <replaceable>str</replaceable> precisely, otherwise returns
+  <literal>null</literal>.  Each item in the list is a regex group.
+
+<programlisting>
+builtins.match "ab" "abc"
+</programlisting>
+
+Evaluates to <literal>null</literal>.
+
+<programlisting>
+builtins.match "abc" "abc"
+</programlisting>
+
+Evaluates to <literal>[ ]</literal>.
+
+<programlisting>
+builtins.match "a(b)(c)" "abc"
+</programlisting>
+
+Evaluates to <literal>[ "b" "c" ]</literal>.
+
+<programlisting>
+builtins.match "[[:space:]]+([[:upper:]]+)[[:space:]]+" "  FOO   "
+</programlisting>
+
+Evaluates to <literal>[ "foo" ]</literal>.
+
+  </para></listitem>
+  </varlistentry>
+
   <varlistentry><term><function>builtins.mul</function>
   <replaceable>e1</replaceable> <replaceable>e2</replaceable></term>
 
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 9250a9b1778f..fc039a8e52b5 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -9,6 +9,7 @@
 #include "finally.hh"
 #include "compression.hh"
 #include "json.hh"
+#include "nar-info.hh"
 
 #include <algorithm>
 #include <iostream>
@@ -121,8 +122,6 @@ protected:
     /* Whether the goal is finished. */
     ExitCode exitCode;
 
-    Activity act;
-
     Goal(Worker & worker) : worker(worker)
     {
         nrFailed = nrNoSubstituters = nrIncompleteClosure = 0;
@@ -244,6 +243,10 @@ private:
 
 public:
 
+    const Activity act;
+    const Activity actDerivations;
+    const Activity actSubstitutions;
+
     /* Set if at least one derivation had a BuildError (i.e. permanent
        failure). */
     bool permanentFailure;
@@ -255,6 +258,20 @@ public:
 
     std::unique_ptr<HookInstance> hook;
 
+    uint64_t expectedBuilds = 0;
+    uint64_t doneBuilds = 0;
+    uint64_t failedBuilds = 0;
+    uint64_t runningBuilds = 0;
+
+    uint64_t expectedSubstitutions = 0;
+    uint64_t doneSubstitutions = 0;
+    uint64_t failedSubstitutions = 0;
+    uint64_t runningSubstitutions = 0;
+    uint64_t expectedDownloadSize = 0;
+    uint64_t doneDownloadSize = 0;
+    uint64_t expectedNarSize = 0;
+    uint64_t doneNarSize = 0;
+
     Worker(LocalStore & store);
     ~Worker();
 
@@ -313,6 +330,14 @@ public:
     bool pathContentsGood(const Path & path);
 
     void markContentsGood(const Path & path);
+
+    void updateProgress()
+    {
+        actDerivations.progress(doneBuilds, expectedBuilds + doneBuilds, runningBuilds, failedBuilds);
+        actSubstitutions.progress(doneSubstitutions, expectedSubstitutions + doneSubstitutions, runningSubstitutions, failedSubstitutions);
+        act.setExpected(actDownload, expectedDownloadSize + doneDownloadSize);
+        act.setExpected(actCopyPath, expectedNarSize + doneNarSize);
+    }
 };
 
 
@@ -810,6 +835,10 @@ private:
 
     const static Path homeDir;
 
+    std::unique_ptr<MaintainCount<uint64_t>> mcExpectedBuilds, mcRunningBuilds;
+
+    std::unique_ptr<Activity> act;
+
 public:
     DerivationGoal(const Path & drvPath, const StringSet & wantedOutputs,
         Worker & worker, BuildMode buildMode = bmNormal);
@@ -907,7 +936,6 @@ private:
 
     void amDone(ExitCode result) override
     {
-        logger->event(evBuildFinished, act, result == ecSuccess);
         Goal::amDone(result);
     }
 
@@ -930,7 +958,8 @@ DerivationGoal::DerivationGoal(const Path & drvPath, const StringSet & wantedOut
     name = (format("building of '%1%'") % drvPath).str();
     trace("created");
 
-    logger->event(evBuildCreated, act, drvPath);
+    mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
+    worker.updateProgress();
 }
 
 
@@ -946,7 +975,8 @@ DerivationGoal::DerivationGoal(const Path & drvPath, const BasicDerivation & drv
     name = (format("building of %1%") % showPaths(drv.outputPaths())).str();
     trace("created");
 
-    logger->event(evBuildCreated, act, drvPath);
+    mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
+    worker.updateProgress();
 
     /* Prevent the .chroot directory from being
        garbage-collected. (See isActiveTempFile() in gc.cc.) */
@@ -1355,6 +1385,12 @@ void DerivationGoal::tryToBuild()
        supported for local builds. */
     bool buildLocally = buildMode != bmNormal || drv->willBuildLocally();
 
+    auto started = [&]() {
+        act = std::make_unique<Activity>(*logger, actBuild, fmt("building '%s'", drvPath));
+        mcRunningBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.runningBuilds);
+        worker.updateProgress();
+    };
+
     /* Is the build hook willing to accept this job? */
     if (!buildLocally) {
         switch (tryBuildHook()) {
@@ -1363,6 +1399,7 @@ void DerivationGoal::tryToBuild()
                    EOF from the hook. */
                 result.startTime = time(0); // inexact
                 state = &DerivationGoal::buildDone;
+                started();
                 return;
             case rpPostpone:
                 /* Not now; wait until at least one child finishes or
@@ -1403,6 +1440,8 @@ void DerivationGoal::tryToBuild()
     /* This state will be reached when we get EOF on the child's
        log pipe. */
     state = &DerivationGoal::buildDone;
+
+    started();
 }
 
 
@@ -2128,8 +2167,6 @@ void DerivationGoal::startBuilder()
         }
         debug(msg);
     }
-
-    logger->event(evBuildStarted, act);
 }
 
 
@@ -3220,7 +3257,7 @@ void DerivationGoal::flushLine()
         logTail.push_back(currentLogLine);
         if (logTail.size() > settings.logLines) logTail.pop_front();
     }
-    logger->event(evBuildOutput, act, currentLogLine);
+    act->result(resBuildLogLine, currentLogLine);
     currentLogLine = "";
     currentLogLinePos = 0;
 }
@@ -3263,6 +3300,19 @@ void DerivationGoal::done(BuildResult::Status status, const string & msg)
         worker.timedOut = true;
     if (result.status == BuildResult::PermanentFailure)
         worker.permanentFailure = true;
+
+    mcExpectedBuilds.reset();
+    mcRunningBuilds.reset();
+
+    if (result.success()) {
+        if (status == BuildResult::Built)
+            worker.doneBuilds++;
+    } else {
+        if (status != BuildResult::DependencyFailed)
+            worker.failedBuilds++;
+    }
+
+    worker.updateProgress();
 }
 
 
@@ -3304,6 +3354,9 @@ private:
        storePath when doing a repair. */
     Path destPath;
 
+    std::unique_ptr<MaintainCount<uint64_t>> maintainExpectedSubstitutions,
+        maintainRunningSubstitutions, maintainExpectedNar, maintainExpectedDownload;
+
     typedef void (SubstitutionGoal::*GoalState)();
     GoalState state;
 
@@ -3338,7 +3391,6 @@ public:
 
     void amDone(ExitCode result) override
     {
-        logger->event(evSubstitutionFinished, act, result == ecSuccess);
         Goal::amDone(result);
     }
 };
@@ -3353,7 +3405,7 @@ SubstitutionGoal::SubstitutionGoal(const Path & storePath, Worker & worker, Repa
     state = &SubstitutionGoal::init;
     name = (format("substitution of '%1%'") % storePath).str();
     trace("created");
-    logger->event(evSubstitutionCreated, act, storePath);
+    maintainExpectedSubstitutions = std::make_unique<MaintainCount<uint64_t>>(worker.expectedSubstitutions);
 }
 
 
@@ -3411,6 +3463,12 @@ void SubstitutionGoal::tryNext()
            In that case the calling derivation should just do a
            build. */
         amDone(hasSubstitute ? ecFailed : ecNoSubstituters);
+
+        if (hasSubstitute) {
+            worker.failedSubstitutions++;
+            worker.updateProgress();
+        }
+
         return;
     }
 
@@ -3430,6 +3488,18 @@ void SubstitutionGoal::tryNext()
         return;
     }
 
+    /* Update the total expected download size. */
+    auto narInfo = std::dynamic_pointer_cast<const NarInfo>(info);
+
+    maintainExpectedNar = std::make_unique<MaintainCount<uint64_t>>(worker.expectedNarSize, narInfo->narSize);
+
+    maintainExpectedDownload =
+        narInfo && narInfo->fileSize
+        ? std::make_unique<MaintainCount<uint64_t>>(worker.expectedDownloadSize, narInfo->fileSize)
+        : nullptr;
+
+    worker.updateProgress();
+
     hasSubstitute = true;
 
     /* Bail out early if this substituter lacks a valid
@@ -3489,7 +3559,8 @@ void SubstitutionGoal::tryToRun()
 
     printInfo(format("fetching path '%1%'...") % storePath);
 
-    logger->event(evSubstitutionStarted, act);
+    maintainRunningSubstitutions = std::make_unique<MaintainCount<uint64_t>>(worker.runningSubstitutions);
+    worker.updateProgress();
 
     outPipe.create();
 
@@ -3538,6 +3609,22 @@ void SubstitutionGoal::finished()
     printMsg(lvlChatty,
         format("substitution of path '%1%' succeeded") % storePath);
 
+    maintainRunningSubstitutions.reset();
+
+    maintainExpectedSubstitutions.reset();
+    worker.doneSubstitutions++;
+
+    if (maintainExpectedDownload) {
+        auto fileSize = maintainExpectedDownload->delta;
+        maintainExpectedDownload.reset();
+        worker.doneDownloadSize += fileSize;
+    }
+
+    worker.doneNarSize += maintainExpectedNar->delta;
+    maintainExpectedNar.reset();
+
+    worker.updateProgress();
+
     amDone(ecSuccess);
 }
 
@@ -3560,7 +3647,10 @@ static bool working = false;
 
 
 Worker::Worker(LocalStore & store)
-    : store(store)
+    : act(*logger, actRealise)
+    , actDerivations(*logger, actBuilds)
+    , actSubstitutions(*logger, actCopyPaths)
+    , store(store)
 {
     /* Debugging: prevent recursive workers. */
     if (working) abort();
@@ -3581,6 +3671,10 @@ Worker::~Worker()
        are in trouble, since goals may call childTerminated() etc. in
        their destructors). */
     topGoals.clear();
+
+    assert(expectedSubstitutions == 0);
+    assert(expectedDownloadSize == 0);
+    assert(expectedNarSize == 0);
 }
 
 
diff --git a/src/libstore/download.cc b/src/libstore/download.cc
index b731297a2086..71b720a3b59e 100644
--- a/src/libstore/download.cc
+++ b/src/libstore/download.cc
@@ -83,12 +83,12 @@ struct CurlDownloader : public Downloader
         std::string encoding;
 
         DownloadItem(CurlDownloader & downloader, const DownloadRequest & request)
-            : downloader(downloader), request(request)
+            : downloader(downloader)
+            , request(request)
+            , act(*logger, actDownload, fmt("downloading '%s'", request.uri))
         {
             if (!request.expectedETag.empty())
                 requestHeaders = curl_slist_append(requestHeaders, ("If-None-Match: " + request.expectedETag).c_str());
-
-            logger->event(evDownloadCreated, act, request.uri);
         }
 
         ~DownloadItem()
@@ -105,7 +105,6 @@ struct CurlDownloader : public Downloader
             } catch (...) {
                 ignoreException();
             }
-            logger->event(evDownloadDestroyed, act);
         }
 
         template<class T>
@@ -168,7 +167,7 @@ struct CurlDownloader : public Downloader
 
         int progressCallback(double dltotal, double dlnow)
         {
-            logger->event(evDownloadProgress, act, dltotal, dlnow);
+            act.progress(dlnow, dltotal);
             return _isInterrupted;
         }
 
@@ -267,7 +266,7 @@ struct CurlDownloader : public Downloader
                 try {
                     result.data = decodeContent(encoding, ref<std::string>(result.data));
                     callSuccess(success, failure, const_cast<const DownloadResult &>(result));
-                    logger->event(evDownloadSucceeded, act, result.data->size());
+                    act.progress(result.data->size(), result.data->size());
                 } catch (...) {
                     done = true;
                     callFailure(failure, std::current_exception());
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 65fe575d2536..855a7c99aed6 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -135,7 +135,6 @@ struct LegacySSHStore : public Store
 
         if (readInt(conn->from) != 1)
             throw Error("failed to add path '%s' to remote host '%s', info.path, host");
-
     }
 
     void narFromPath(const Path & path, Sink & sink) override
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 551c6b506fb1..2af1bfbb3892 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -251,7 +251,7 @@ private:
 
     InodeHash loadInodeHash();
     Strings readDirectoryIgnoringInodes(const Path & path, const InodeHash & inodeHash);
-    void optimisePath_(OptimiseStats & stats, const Path & path, InodeHash & inodeHash);
+    void optimisePath_(Activity * act, OptimiseStats & stats, const Path & path, InodeHash & inodeHash);
 
     // Internal versions that are not wrapped in retry_sqlite.
     bool isValidPath_(State & state, const Path & path);
diff --git a/src/libstore/optimise-store.cc b/src/libstore/optimise-store.cc
index b736307b31b4..f1325ba5a1ce 100644
--- a/src/libstore/optimise-store.cc
+++ b/src/libstore/optimise-store.cc
@@ -89,7 +89,8 @@ Strings LocalStore::readDirectoryIgnoringInodes(const Path & path, const InodeHa
 }
 
 
-void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path, InodeHash & inodeHash)
+void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
+    const Path & path, InodeHash & inodeHash)
 {
     checkInterrupt();
 
@@ -114,7 +115,7 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path, InodeHa
     if (S_ISDIR(st.st_mode)) {
         Strings names = readDirectoryIgnoringInodes(path, inodeHash);
         for (auto & i : names)
-            optimisePath_(stats, path + "/" + i, inodeHash);
+            optimisePath_(act, stats, path + "/" + i, inodeHash);
         return;
     }
 
@@ -244,19 +245,32 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path, InodeHa
     stats.filesLinked++;
     stats.bytesFreed += st.st_size;
     stats.blocksFreed += st.st_blocks;
+
+    if (act)
+        act->result(resFileLinked, st.st_size, st.st_blocks);
 }
 
 
 void LocalStore::optimiseStore(OptimiseStats & stats)
 {
+    Activity act(*logger, actOptimiseStore);
+
     PathSet paths = queryAllValidPaths();
     InodeHash inodeHash = loadInodeHash();
 
+    act.progress(0, paths.size());
+
+    uint64_t done = 0;
+
     for (auto & i : paths) {
         addTempRoot(i);
         if (!isValidPath(i)) continue; /* path was GC'ed, probably */
-        //Activity act(*logger, lvlChatty, format("hashing files in '%1%'") % i);
-        optimisePath_(stats, realStoreDir + "/" + baseNameOf(i), inodeHash);
+        {
+            Activity act(*logger, actUnknown, fmt("optimising path '%s'", i));
+            optimisePath_(&act, stats, realStoreDir + "/" + baseNameOf(i), inodeHash);
+        }
+        done++;
+        act.progress(done, paths.size());
     }
 }
 
@@ -271,7 +285,7 @@ void LocalStore::optimiseStore()
 
     optimiseStore(stats);
 
-    printError(
+    printInfo(
         format("%1% freed by hard-linking %2% files")
         % showBytes(stats.bytesFreed)
         % stats.filesLinked);
@@ -282,7 +296,7 @@ void LocalStore::optimisePath(const Path & path)
     OptimiseStats stats;
     InodeHash inodeHash;
 
-    if (settings.autoOptimiseStore) optimisePath_(stats, path, inodeHash);
+    if (settings.autoOptimiseStore) optimisePath_(nullptr, stats, path, inodeHash);
 }
 
 
diff --git a/src/libstore/ssh.cc b/src/libstore/ssh.cc
index 776ffdb83431..7ff7a9bffc49 100644
--- a/src/libstore/ssh.cc
+++ b/src/libstore/ssh.cc
@@ -2,6 +2,17 @@
 
 namespace nix {
 
+SSHMaster::SSHMaster(const std::string & host, const std::string & keyFile, bool useMaster, bool compress, int logFD)
+    : host(host)
+    , keyFile(keyFile)
+    , useMaster(useMaster)
+    , compress(compress)
+    , logFD(logFD)
+{
+    if (host == "" || hasPrefix(host, "-"))
+        throw Error("invalid SSH host name '%s'", host);
+}
+
 void SSHMaster::addCommonSSHOpts(Strings & args)
 {
     for (auto & i : tokenizeString<Strings>(getEnv("NIX_SSHOPTS")))
diff --git a/src/libstore/ssh.hh b/src/libstore/ssh.hh
index 18dea227ad1f..1268e6d00054 100644
--- a/src/libstore/ssh.hh
+++ b/src/libstore/ssh.hh
@@ -28,14 +28,7 @@ private:
 
 public:
 
-    SSHMaster(const std::string & host, const std::string & keyFile, bool useMaster, bool compress, int logFD = -1)
-        : host(host)
-        , keyFile(keyFile)
-        , useMaster(useMaster)
-        , compress(compress)
-        , logFD(logFD)
-    {
-    }
+    SSHMaster(const std::string & host, const std::string & keyFile, bool useMaster, bool compress, int logFD = -1);
 
     struct Connection
     {
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index dd87a046e380..f520210615a3 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -565,9 +565,30 @@ void Store::buildPaths(const PathSet & paths, BuildMode buildMode)
 void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
     const Path & storePath, RepairFlag repair, CheckSigsFlag checkSigs)
 {
+    Activity act(*logger, actCopyPath, fmt("copying path '%s'", storePath));
+
     auto info = srcStore->queryPathInfo(storePath);
 
-    StringSink sink;
+    uint64_t total = 0;
+
+    auto progress = [&](size_t len) {
+        total += len;
+        act.progress(total, info->narSize);
+    };
+
+    struct MyStringSink : StringSink
+    {
+        typedef std::function<void(size_t)> Callback;
+        Callback callback;
+        MyStringSink(Callback callback) : callback(callback) { }
+        void operator () (const unsigned char * data, size_t len) override
+        {
+            StringSink::operator ()(data, len);
+            callback(len);
+        };
+    };
+
+    MyStringSink sink(progress);
     srcStore->narFromPath({storePath}, sink);
 
     if (!info->narHash && !checkSigs) {
@@ -600,23 +621,47 @@ void copyPaths(ref<Store> srcStore, ref<Store> dstStore, const PathSet & storePa
     for (auto & path : storePaths)
         if (!valid.count(path)) missing.insert(path);
 
+    Activity act(*logger, actCopyPaths, fmt("copying %d paths", missing.size()));
+
+    std::atomic<size_t> nrDone{0};
+    std::atomic<uint64_t> bytesExpected{0};
+    std::atomic<uint64_t> nrRunning{0};
+
+    auto showProgress = [&]() {
+        act.progress(nrDone, missing.size(), nrRunning);
+    };
+
     ThreadPool pool;
 
     processGraph<Path>(pool,
         PathSet(missing.begin(), missing.end()),
 
         [&](const Path & storePath) {
-            if (dstStore->isValidPath(storePath)) return PathSet();
-            return srcStore->queryPathInfo(storePath)->references;
+            if (dstStore->isValidPath(storePath)) {
+                nrDone++;
+                showProgress();
+                return PathSet();
+            }
+
+            auto info = srcStore->queryPathInfo(storePath);
+
+            bytesExpected += info->narSize;
+            act.setExpected(actCopyPath, bytesExpected);
+
+            return info->references;
         },
 
         [&](const Path & storePath) {
             checkInterrupt();
 
             if (!dstStore->isValidPath(storePath)) {
-                printInfo("copying '%s'...", storePath);
+                MaintainCount<decltype(nrRunning)> mc(nrRunning);
+                showProgress();
                 copyStorePath(srcStore, dstStore, storePath, repair, checkSigs);
             }
+
+            nrDone++;
+            showProgress();
         });
 }
 
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index 51b57a8f4e97..ea1deb924e67 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -56,6 +56,8 @@ static void dumpContents(const Path & path, size_t size,
 
 static void dump(const Path & path, Sink & sink, PathFilter & filter)
 {
+    checkInterrupt();
+
     struct stat st;
     if (lstat(path.c_str(), &st))
         throw SysError(format("getting attributes of path '%1%'") % path);
diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index 43245f61c601..900f24e4cbdf 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -43,10 +43,6 @@ public:
 
         writeToStderr(prefix + (tty ? fs.s : filterANSIEscapes(fs.s)) + "\n");
     }
-
-    void event(const Event & ev) override
-    {
-    }
 };
 
 Verbosity verbosity = lvlInfo;
@@ -78,6 +74,10 @@ Logger * makeDefaultLogger()
 
 std::atomic<uint64_t> nextId{(uint64_t) getpid() << 32};
 
-Activity::Activity() : id(nextId++) { };
+Activity::Activity(Logger & logger, ActivityType type, const std::string & s)
+    : logger(logger), id(nextId++)
+{
+    logger.startActivity(id, type, s);
+}
 
 }
diff --git a/src/libutil/logging.hh b/src/libutil/logging.hh
index 9ef6e3ee30e4..1e0c735676b6 100644
--- a/src/libutil/logging.hh
+++ b/src/libutil/logging.hh
@@ -13,32 +13,52 @@ typedef enum {
     lvlVomit
 } Verbosity;
 
-class Activity
-{
-public:
-    typedef uint64_t t;
-    const t id;
-    Activity();
-    Activity(const Activity & act) : id(act.id) { };
-    Activity(uint64_t id) : id(id) { };
-};
+typedef enum {
+    actUnknown = 0,
+    actCopyPath = 100,
+    actDownload = 101,
+    actRealise = 102,
+    actCopyPaths = 103,
+    actBuilds = 104,
+    actBuild = 105,
+    actOptimiseStore = 106,
+    actVerifyPaths = 107,
+} ActivityType;
 
 typedef enum {
-    evBuildCreated = 0,
-    evBuildStarted = 1,
-    evBuildOutput = 2,
-    evBuildFinished = 3,
-    evDownloadCreated = 4,
-    evDownloadDestroyed = 5,
-    evDownloadProgress = 6,
-    evDownloadSucceeded = 7,
-    evSubstitutionCreated = 8,
-    evSubstitutionStarted = 9,
-    evSubstitutionFinished = 10,
-} EventType;
-
-struct Event
+    resFileLinked = 100,
+    resBuildLogLine = 101,
+    resUntrustedPath = 102,
+    resCorruptedPath = 103,
+} ResultType;
+
+typedef uint64_t ActivityId;
+
+class Logger
 {
+    friend class Activity;
+
+public:
+
+    virtual ~Logger() { }
+
+    virtual void log(Verbosity lvl, const FormatOrString & fs) = 0;
+
+    void log(const FormatOrString & fs)
+    {
+        log(lvlInfo, fs);
+    }
+
+    virtual void warn(const std::string & msg);
+
+    virtual void startActivity(ActivityId act, ActivityType type, const std::string & s) { };
+
+    virtual void stopActivity(ActivityId act) { };
+
+    virtual void progress(ActivityId act, uint64_t done = 0, uint64_t expected = 0, uint64_t running = 0, uint64_t failed = 0) { };
+
+    virtual void setExpected(ActivityId act, ActivityType type, uint64_t expected) { };
+
     struct Field
     {
         // FIXME: use std::variant.
@@ -48,56 +68,37 @@ struct Event
         Field(const std::string & s) : type(tString), s(s) { }
         Field(const char * s) : type(tString), s(s) { }
         Field(const uint64_t & i) : type(tInt), i(i) { }
-        Field(const Activity & act) : type(tInt), i(act.id) { }
     };
 
-    typedef std::vector<Field> Fields;
-
-    EventType type;
-    Fields fields;
-
-    std::string getS(size_t n) const
-    {
-        assert(n < fields.size());
-        assert(fields[n].type == Field::tString);
-        return fields[n].s;
-    }
-
-    uint64_t getI(size_t n) const
-    {
-        assert(n < fields.size());
-        assert(fields[n].type == Field::tInt);
-        return fields[n].i;
-    }
+    virtual void result(ActivityId act, ResultType type, const std::vector<Field> & fields) { };
 };
 
-class Logger
+struct Activity
 {
-    friend class Activity;
+    Logger & logger;
 
-public:
+    const ActivityId id;
 
-    virtual ~Logger() { }
+    Activity(Logger & logger, ActivityType type, const std::string & s = "");
 
-    virtual void log(Verbosity lvl, const FormatOrString & fs) = 0;
+    ~Activity()
+    { logger.stopActivity(id); }
 
-    void log(const FormatOrString & fs)
-    {
-        log(lvlInfo, fs);
-    }
+    void progress(uint64_t done = 0, uint64_t expected = 0, uint64_t running = 0, uint64_t failed = 0) const
+    { logger.progress(id, done, expected, running, failed); }
 
-    virtual void warn(const std::string & msg);
+    void setExpected(ActivityType type2, uint64_t expected) const
+    { logger.setExpected(id, type2, expected); }
 
     template<typename... Args>
-    void event(EventType type, const Args & ... args)
+    void result(ResultType type, const Args & ... args)
     {
-        Event ev;
-        ev.type = type;
-        nop{(ev.fields.emplace_back(Event::Field(args)), 1)...};
-        event(ev);
+        std::vector<Logger::Field> fields;
+        nop{(fields.emplace_back(Logger::Field(args)), 1)...};
+        logger.result(id, type, fields);
     }
 
-    virtual void event(const Event & ev) = 0;
+    friend class Logger;
 };
 
 extern Logger * logger;
diff --git a/src/libutil/types.hh b/src/libutil/types.hh
index 9f32d31addbf..92bf469b5c6f 100644
--- a/src/libutil/types.hh
+++ b/src/libutil/types.hh
@@ -70,6 +70,7 @@ template<typename... Args>
 inline std::string fmt(const std::string & fs, Args... args)
 {
     boost::format f(fs);
+    f.exceptions(boost::io::all_error_bits ^ boost::io::too_many_args_bit);
     nop{boost::io::detail::feed(f, args)...};
     return f.str();
 }
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index f37f2c5d1be5..35909c8d5b31 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -462,4 +462,18 @@ struct ReceiveInterrupts
     { }
 };
 
+
+
+/* A RAII helper that increments a counter on construction and
+   decrements it on destruction. */
+template<typename T>
+struct MaintainCount
+{
+    T & counter;
+    long delta;
+    MaintainCount(T & counter, long delta = 1) : counter(counter), delta(delta) { counter += delta; }
+    ~MaintainCount() { counter -= delta; }
+};
+
+
 }
diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index 2b223c882647..7e6f3aa25b5e 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -81,10 +81,6 @@ class TunnelLogger : public Logger
         } else
             defaultLogger->log(lvl, fs);
     }
-
-    void event(const Event & ev) override
-    {
-    }
 };
 
 
diff --git a/src/nix/copy.cc b/src/nix/copy.cc
index 9f1a80d07bea..d9e6c949352b 100644
--- a/src/nix/copy.cc
+++ b/src/nix/copy.cc
@@ -12,10 +12,17 @@ struct CmdCopy : StorePathsCommand
 {
     std::string srcUri, dstUri;
 
+    CheckSigsFlag checkSigs = CheckSigs;
+
     CmdCopy()
     {
         mkFlag(0, "from", "store-uri", "URI of the source Nix store", &srcUri);
         mkFlag(0, "to", "store-uri", "URI of the destination Nix store", &dstUri);
+
+        mkFlag()
+            .longName("no-check-sigs")
+            .description("do not require that paths are signed by trusted keys")
+            .handler([&](Strings ss) { checkSigs = NoCheckSigs; });
     }
 
     std::string name() override
@@ -50,7 +57,8 @@ struct CmdCopy : StorePathsCommand
 
         ref<Store> dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
 
-        copyPaths(srcStore, dstStore, PathSet(storePaths.begin(), storePaths.end()));
+        copyPaths(srcStore, dstStore, PathSet(storePaths.begin(), storePaths.end()),
+            NoRepair, checkSigs);
     }
 };
 
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 54c9f7841fe0..9d812fee47ec 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -229,7 +229,7 @@ std::vector<std::shared_ptr<Installable>> InstallablesCommand::parseInstallables
 
 PathSet InstallablesCommand::toStorePaths(ref<Store> store, ToStorePathsMode mode)
 {
-    if (mode != DryRun)
+    if (mode != Build)
         settings.readOnlyMode = true;
 
     PathSet outPaths, buildables;
diff --git a/src/nix/optimise-store.cc b/src/nix/optimise-store.cc
new file mode 100644
index 000000000000..725fb75a19ec
--- /dev/null
+++ b/src/nix/optimise-store.cc
@@ -0,0 +1,41 @@
+#include "command.hh"
+#include "shared.hh"
+#include "store-api.hh"
+
+#include <atomic>
+
+using namespace nix;
+
+struct CmdOptimiseStore : StoreCommand
+{
+    CmdOptimiseStore()
+    {
+    }
+
+    std::string name() override
+    {
+        return "optimise-store";
+    }
+
+    std::string description() override
+    {
+        return "replace identical files in the store by hard links";
+    }
+
+    Examples examples() override
+    {
+        return {
+            Example{
+                "To optimise the Nix store:",
+                "nix optimise-store"
+            },
+        };
+    }
+
+    void run(ref<Store> store) override
+    {
+        store->optimiseStore();
+    }
+};
+
+static RegisterCommand r1(make_ref<CmdOptimiseStore>());
diff --git a/src/nix/progress-bar.cc b/src/nix/progress-bar.cc
index 2ecbea8eeea8..1616c420551a 100644
--- a/src/nix/progress-bar.cc
+++ b/src/nix/progress-bar.cc
@@ -8,8 +8,24 @@
 
 #include <sys/ioctl.h>
 
+#include <iostream>
+
 namespace nix {
 
+static std::string getS(const std::vector<Logger::Field> & fields, size_t n)
+{
+    assert(n < fields.size());
+    assert(fields[n].type == Logger::Field::tString);
+    return fields[n].s;
+}
+
+static uint64_t getI(const std::vector<Logger::Field> & fields, size_t n)
+{
+    assert(n < fields.size());
+    assert(fields[n].type == Logger::Field::tInt);
+    return fields[n].i;
+}
+
 class ProgressBar : public Logger
 {
 private:
@@ -17,29 +33,32 @@ private:
     struct ActInfo
     {
         std::string s, s2;
+        ActivityType type = actUnknown;
+        uint64_t done = 0;
+        uint64_t expected = 0;
+        uint64_t running = 0;
+        uint64_t failed = 0;
+        std::map<ActivityType, uint64_t> expectedByType;
     };
 
-    struct DownloadInfo
+    struct ActivitiesByType
     {
-        std::string uri;
-        uint64_t current = 0;
+        std::map<ActivityId, std::list<ActInfo>::iterator> its;
+        uint64_t done = 0;
         uint64_t expected = 0;
-        DownloadInfo(const std::string & uri) : uri(uri) { }
+        uint64_t failed = 0;
     };
 
     struct State
     {
-        std::map<Activity::t, Path> builds;
-        std::set<Activity::t> runningBuilds;
-        uint64_t succeededBuilds = 0;
-        uint64_t failedBuilds = 0;
-        std::map<Activity::t, Path> substitutions;
-        std::set<Activity::t> runningSubstitutions;
-        uint64_t succeededSubstitutions = 0;
-        uint64_t downloadedBytes = 0; // finished downloads
-        std::map<Activity::t, DownloadInfo> downloads;
         std::list<ActInfo> activities;
-        std::map<Activity::t, std::list<ActInfo>::iterator> its;
+        std::map<ActivityId, std::list<ActInfo>::iterator> its;
+
+        std::map<ActivityType, ActivitiesByType> activitiesByType;
+
+        uint64_t filesLinked = 0, bytesLinked = 0;
+
+        uint64_t corruptedPaths = 0, untrustedPaths = 0;
     };
 
     Sync<State> state_;
@@ -58,7 +77,10 @@ public:
     ~ProgressBar()
     {
         auto state(state_.lock());
+        std::string status = getStatus(*state);
         writeToStderr("\r\e[K");
+        if (status != "")
+            writeToStderr("[" + status + "]\n");
     }
 
     void log(Verbosity lvl, const FormatOrString & fs) override
@@ -73,30 +95,102 @@ public:
         update(state);
     }
 
-    void createActivity(State & state, Activity::t activity, const std::string & s)
+    void startActivity(ActivityId act, ActivityType type, const std::string & s) override
     {
-        state.activities.emplace_back(ActInfo{s});
-        state.its.emplace(activity, std::prev(state.activities.end()));
+        auto state(state_.lock());
+
+        state->activities.emplace_back(ActInfo{s, "", type});
+        auto i = std::prev(state->activities.end());
+        state->its.emplace(act, i);
+        state->activitiesByType[type].its.emplace(act, i);
+
+        update(*state);
     }
 
-    void deleteActivity(State & state, Activity::t activity)
+    void stopActivity(ActivityId act) override
     {
-        auto i = state.its.find(activity);
-        if (i != state.its.end()) {
-            state.activities.erase(i->second);
-            state.its.erase(i);
+        auto state(state_.lock());
+
+        auto i = state->its.find(act);
+        if (i != state->its.end()) {
+            auto & actByType = state->activitiesByType[i->second->type];
+            actByType.done += i->second->done;
+            actByType.failed += i->second->failed;
+
+            for (auto & j : i->second->expectedByType)
+                state->activitiesByType[j.first].expected -= j.second;
+
+            actByType.its.erase(act);
+            state->activities.erase(i->second);
+            state->its.erase(i);
         }
+
+        update(*state);
+    }
+
+    void progress(ActivityId act, uint64_t done = 0, uint64_t expected = 0, uint64_t running = 0, uint64_t failed = 0) override
+    {
+        auto state(state_.lock());
+
+        auto i = state->its.find(act);
+        assert(i != state->its.end());
+        ActInfo & actInfo = *i->second;
+        actInfo.done = done;
+        actInfo.expected = expected;
+        actInfo.running = running;
+        actInfo.failed = failed;
+
+        update(*state);
+    }
+
+    void setExpected(ActivityId act, ActivityType type, uint64_t expected) override
+    {
+        auto state(state_.lock());
+
+        auto i = state->its.find(act);
+        assert(i != state->its.end());
+        ActInfo & actInfo = *i->second;
+        auto & j = actInfo.expectedByType[type];
+        state->activitiesByType[type].expected -= j;
+        j = expected;
+        state->activitiesByType[type].expected += j;
+
+        update(*state);
     }
 
-    void updateActivity(State & state, Activity::t activity, const std::string & s2)
+    void result(ActivityId act, ResultType type, const std::vector<Field> & fields) override
     {
-        auto i = state.its.find(activity);
-        assert(i != state.its.end());
-        ActInfo info = *i->second;
-        state.activities.erase(i->second);
-        info.s2 = s2;
-        state.activities.emplace_back(info);
-        i->second = std::prev(state.activities.end());
+        auto state(state_.lock());
+
+        if (type == resFileLinked) {
+            state->filesLinked++;
+            state->bytesLinked += getI(fields, 0);
+            update(*state);
+        }
+
+        else if (type == resBuildLogLine) {
+            auto s2 = trim(getS(fields, 0));
+            if (!s2.empty()) {
+                auto i = state->its.find(act);
+                assert(i != state->its.end());
+                ActInfo info = *i->second;
+                state->activities.erase(i->second);
+                info.s2 = s2;
+                state->activities.emplace_back(info);
+                i->second = std::prev(state->activities.end());
+                update(*state);
+            }
+        }
+
+        else if (type == resUntrustedPath) {
+            state->untrustedPaths++;
+            update(*state);
+        }
+
+        else if (type == resCorruptedPath) {
+            state->corruptedPaths++;
+            update(*state);
+        }
     }
 
     void update()
@@ -119,10 +213,16 @@ public:
         if (!state.activities.empty()) {
             if (!status.empty()) line += " ";
             auto i = state.activities.rbegin();
-            line += i->s;
-            if (!i->s2.empty()) {
-                line += ": ";
-                line += i->s2;
+
+            while (i != state.activities.rend() && i->s.empty() && i->s2.empty())
+                ++i;
+
+            if (i != state.activities.rend()) {
+                line += i->s;
+                if (!i->s2.empty()) {
+                    if (!i->s.empty()) line += ": ";
+                    line += i->s2;
+                }
             }
         }
 
@@ -132,154 +232,85 @@ public:
 
     std::string getStatus(State & state)
     {
+        auto MiB = 1024.0 * 1024.0;
+
         std::string res;
 
-        if (state.failedBuilds) {
-            if (!res.empty()) res += ", ";
-            res += fmt(ANSI_RED "%d failed" ANSI_NORMAL, state.failedBuilds);
-        }
+        auto renderActivity = [&](ActivityType type, const std::string & itemFmt, const std::string & numberFmt = "%d", double unit = 1) {
+            auto & act = state.activitiesByType[type];
+            uint64_t done = act.done, expected = act.done, running = 0, failed = act.failed;
+            for (auto & j : act.its) {
+                done += j.second->done;
+                expected += j.second->expected;
+                running += j.second->running;
+                failed += j.second->failed;
+            }
 
-        if (!state.builds.empty() || state.succeededBuilds)
-        {
-            if (!res.empty()) res += ", ";
-            if (!state.runningBuilds.empty())
-                res += fmt(ANSI_BLUE "%d" "/" ANSI_NORMAL, state.runningBuilds.size());
-            res += fmt(ANSI_GREEN "%d/%d built" ANSI_NORMAL,
-                state.succeededBuilds, state.succeededBuilds + state.builds.size());
-        }
+            expected = std::max(expected, act.expected);
 
-        if (!state.substitutions.empty() || state.succeededSubstitutions) {
-            if (!res.empty()) res += ", ";
-            if (!state.runningSubstitutions.empty())
-                res += fmt(ANSI_BLUE "%d" "/" ANSI_NORMAL, state.runningSubstitutions.size());
-            res += fmt(ANSI_GREEN "%d/%d fetched" ANSI_NORMAL,
-                state.succeededSubstitutions,
-                state.succeededSubstitutions + state.substitutions.size());
-        }
+            std::string s;
 
-        if (!state.downloads.empty() || state.downloadedBytes) {
-            if (!res.empty()) res += ", ";
-            uint64_t expected = state.downloadedBytes, current = state.downloadedBytes;
-            for (auto & i : state.downloads) {
-                expected += i.second.expected;
-                current += i.second.current;
-            }
-            res += fmt("%1$.0f/%2$.0f KiB", current / 1024.0, expected / 1024.0);
-        }
+            if (running || done || expected || failed) {
+                if (running)
+                    s = fmt(ANSI_BLUE + numberFmt + ANSI_NORMAL "/" ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
+                        running / unit, done / unit, expected / unit);
+                else if (expected != done)
+                    s = fmt(ANSI_GREEN + numberFmt + ANSI_NORMAL "/" + numberFmt,
+                        done / unit, expected / unit);
+                else
+                    s = fmt(done ? ANSI_GREEN + numberFmt + ANSI_NORMAL : numberFmt, done / unit);
+                s = fmt(itemFmt, s);
 
-        return res;
-    }
+                if (failed)
+                    s += fmt(" (" ANSI_RED "%d failed" ANSI_NORMAL ")", failed / unit);
+            }
 
-    void event(const Event & ev) override
-    {
-        if (ev.type == evBuildCreated) {
-            auto state(state_.lock());
-            state->builds[ev.getI(0)] = ev.getS(1);
-            update(*state);
-        }
+            return s;
+        };
 
-        if (ev.type == evBuildStarted) {
-            auto state(state_.lock());
-            Activity::t act = ev.getI(0);
-            state->runningBuilds.insert(act);
-            auto name = storePathToName(state->builds[act]);
-            if (hasSuffix(name, ".drv"))
-                name.resize(name.size() - 4);
-            createActivity(*state, act, fmt("building " ANSI_BOLD "%s" ANSI_NORMAL, name));
-            update(*state);
-        }
+        auto showActivity = [&](ActivityType type, const std::string & itemFmt, const std::string & numberFmt = "%d", double unit = 1) {
+            auto s = renderActivity(type, itemFmt, numberFmt, unit);
+            if (s.empty()) return;
+            if (!res.empty()) res += ", ";
+            res += s;
+        };
 
-        if (ev.type == evBuildFinished) {
-            auto state(state_.lock());
-            Activity::t act = ev.getI(0);
-            if (ev.getI(1)) {
-                if (state->runningBuilds.count(act))
-                    state->succeededBuilds++;
-            } else
-                state->failedBuilds++;
-            state->runningBuilds.erase(act);
-            state->builds.erase(act);
-            deleteActivity(*state, act);
-            update(*state);
-        }
+        showActivity(actBuilds, "%s built");
 
-        if (ev.type == evBuildOutput) {
-            auto state(state_.lock());
-            Activity::t act = ev.getI(0);
-            assert(state->runningBuilds.count(act));
-            updateActivity(*state, act, ev.getS(1));
-            update(*state);
-        }
+        auto s1 = renderActivity(actCopyPaths, "%s copied");
+        auto s2 = renderActivity(actCopyPath, "%s MiB", "%.1f", MiB);
 
-        if (ev.type == evSubstitutionCreated) {
-            auto state(state_.lock());
-            state->substitutions[ev.getI(0)] = ev.getS(1);
-            update(*state);
+        if (!s1.empty() || !s2.empty()) {
+            if (!res.empty()) res += ", ";
+            if (s1.empty()) res += "0 copied"; else res += s1;
+            if (!s2.empty()) { res += " ("; res += s2; res += ')'; }
         }
 
-        if (ev.type == evSubstitutionStarted) {
-            auto state(state_.lock());
-            Activity::t act = ev.getI(0);
-            state->runningSubstitutions.insert(act);
-            auto name = storePathToName(state->substitutions[act]);
-            createActivity(*state, act, fmt("fetching " ANSI_BOLD "%s" ANSI_NORMAL, name));
-            update(*state);
-        }
+        showActivity(actDownload, "%s MiB DL", "%.1f", MiB);
 
-        if (ev.type == evSubstitutionFinished) {
-            auto state(state_.lock());
-            Activity::t act = ev.getI(0);
-            if (ev.getI(1)) {
-                if (state->runningSubstitutions.count(act))
-                    state->succeededSubstitutions++;
+        {
+            auto s = renderActivity(actOptimiseStore, "%s paths optimised");
+            if (s != "") {
+                s += fmt(", %.1f MiB / %d inodes freed", state.bytesLinked / MiB, state.filesLinked);
+                if (!res.empty()) res += ", ";
+                res += s;
             }
-            state->runningSubstitutions.erase(act);
-            state->substitutions.erase(act);
-            deleteActivity(*state, act);
-            update(*state);
         }
 
-        if (ev.type == evDownloadCreated) {
-            auto state(state_.lock());
-            Activity::t act = ev.getI(0);
-            std::string uri = ev.getS(1);
-            state->downloads.emplace(act, DownloadInfo{uri});
-            if (state->runningSubstitutions.empty()) // FIXME: hack
-                createActivity(*state, act, fmt("downloading " ANSI_BOLD "%s" ANSI_NORMAL "", uri));
-            update(*state);
-        }
+        // FIXME: don't show "done" paths in green.
+        showActivity(actVerifyPaths, "%s paths verified");
 
-        if (ev.type == evDownloadProgress) {
-            auto state(state_.lock());
-            Activity::t act = ev.getI(0);
-            auto i = state->downloads.find(act);
-            assert(i != state->downloads.end());
-            i->second.expected = ev.getI(1);
-            i->second.current = ev.getI(2);
-            update(*state);
+        if (state.corruptedPaths) {
+            if (!res.empty()) res += ", ";
+            res += fmt(ANSI_RED "%d corrupted" ANSI_NORMAL, state.corruptedPaths);
         }
 
-        if (ev.type == evDownloadSucceeded) {
-            auto state(state_.lock());
-            Activity::t act = ev.getI(0);
-            auto i = state->downloads.find(act);
-            assert(i != state->downloads.end());
-            state->downloadedBytes += ev.getI(1);
-            state->downloads.erase(i);
-            deleteActivity(*state, act);
-            update(*state);
+        if (state.untrustedPaths) {
+            if (!res.empty()) res += ", ";
+            res += fmt(ANSI_RED "%d untrusted" ANSI_NORMAL, state.untrustedPaths);
         }
 
-        if (ev.type == evDownloadDestroyed) {
-            auto state(state_.lock());
-            Activity::t act = ev.getI(0);
-            auto i = state->downloads.find(act);
-            if (i != state->downloads.end()) {
-                state->downloads.erase(i);
-                deleteActivity(*state, act);
-                update(*state);
-            }
-        }
+        return res;
     }
 };
 
diff --git a/src/nix/verify.cc b/src/nix/verify.cc
index 0d9739314b53..7156341396d3 100644
--- a/src/nix/verify.cc
+++ b/src/nix/verify.cc
@@ -61,16 +61,17 @@ struct CmdVerify : StorePathsCommand
 
         auto publicKeys = getDefaultPublicKeys();
 
+        Activity act(*logger, actVerifyPaths);
+
         std::atomic<size_t> done{0};
         std::atomic<size_t> untrusted{0};
         std::atomic<size_t> corrupted{0};
         std::atomic<size_t> failed{0};
+        std::atomic<size_t> active{0};
 
-        std::string doneLabel("paths checked");
-        std::string untrustedLabel("untrusted");
-        std::string corruptedLabel("corrupted");
-        std::string failedLabel("failed");
-        //logger->setExpected(doneLabel, storePaths.size());
+        auto update = [&]() {
+            act.progress(done, storePaths.size(), active, failed);
+        };
 
         ThreadPool pool;
 
@@ -78,7 +79,10 @@ struct CmdVerify : StorePathsCommand
             try {
                 checkInterrupt();
 
-                //Activity act(*logger, lvlInfo, format("checking '%s'") % storePath);
+                Activity act2(*logger, actUnknown, fmt("checking '%s'", storePath));
+
+                MaintainCount<std::atomic<size_t>> mcActive(active);
+                update();
 
                 auto info = store->queryPathInfo(storePath);
 
@@ -90,8 +94,8 @@ struct CmdVerify : StorePathsCommand
                     auto hash = sink.finish();
 
                     if (hash.first != info->narHash) {
-                        //logger->incProgress(corruptedLabel);
-                        corrupted = 1;
+                        corrupted++;
+                        act2.result(resCorruptedPath, info->path);
                         printError(
                             format("path '%s' was modified! expected hash '%s', got '%s'")
                             % info->path % info->narHash.to_string() % hash.first.to_string());
@@ -142,21 +146,21 @@ struct CmdVerify : StorePathsCommand
                     }
 
                     if (!good) {
-                        //logger->incProgress(untrustedLabel);
                         untrusted++;
+                        act2.result(resUntrustedPath, info->path);
                         printError(format("path '%s' is untrusted") % info->path);
                     }
 
                 }
 
-                //logger->incProgress(doneLabel);
                 done++;
 
             } catch (Error & e) {
                 printError(format(ANSI_RED "error:" ANSI_NORMAL " %s") % e.what());
-                //logger->incProgress(failedLabel);
                 failed++;
             }
+
+            update();
         };
 
         for (auto & storePath : storePaths)
@@ -164,9 +168,6 @@ struct CmdVerify : StorePathsCommand
 
         pool.process();
 
-        printInfo(format("%d paths checked, %d untrusted, %d corrupted, %d failed")
-            % done % untrusted % corrupted % failed);
-
         throw Exit(
             (corrupted ? 1 : 0) |
             (untrusted ? 2 : 0) |