lix/src/nix/run.cc

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#include "command.hh"
#include "common-args.hh"
#include "shared.hh"
#include "store-api.hh"
#include "derivations.hh"
#include "local-store.hh"
#include "finally.hh"
#include "fs-accessor.hh"
#include "progress-bar.hh"
#include "affinity.hh"
#if __linux__
#include <sys/mount.h>
#endif
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#include <queue>
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using namespace nix;
std::string chrootHelperName = "__run_in_chroot";
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struct CmdRun : InstallablesCommand
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{
std::vector<std::string> command = { "bash" };
StringSet keep, unset;
bool ignoreEnvironment = false;
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CmdRun()
{
mkFlag()
.longName("command")
.shortName('c')
.description("command and arguments to be executed; defaults to 'bash'")
.labels({"command", "args"})
.arity(ArityAny)
.handler([&](std::vector<std::string> ss) {
if (ss.empty()) throw UsageError("--command requires at least one argument");
command = ss;
});
mkFlag()
.longName("ignore-environment")
.shortName('i')
.description("clear the entire environment (except those specified with --keep)")
.set(&ignoreEnvironment, true);
mkFlag()
.longName("keep")
.shortName('k')
.description("keep specified environment variable")
.arity(1)
.labels({"name"})
.handler([&](std::vector<std::string> ss) { keep.insert(ss.front()); });
mkFlag()
.longName("unset")
.shortName('u')
.description("unset specified environment variable")
.arity(1)
.labels({"name"})
.handler([&](std::vector<std::string> ss) { unset.insert(ss.front()); });
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}
std::string description() override
{
return "run a shell in which the specified packages are available";
}
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Examples examples() override
{
return {
Example{
"To start a shell providing GNU Hello from NixOS 17.03:",
"nix run -f channel:nixos-17.03 hello"
},
Example{
"To start a shell providing youtube-dl from your 'nixpkgs' channel:",
"nix run nixpkgs.youtube-dl"
},
Example{
"To run GNU Hello:",
"nix run nixpkgs.hello -c hello --greeting 'Hi everybody!'"
},
Example{
"To run GNU Hello in a chroot store:",
"nix run --store ~/my-nix nixpkgs.hello -c hello"
},
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};
}
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void run(ref<Store> store) override
{
auto outPaths = toStorePaths(store, Build, installables);
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auto accessor = store->getFSAccessor();
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if (ignoreEnvironment) {
if (!unset.empty())
throw UsageError("--unset does not make sense with --ignore-environment");
std::map<std::string, std::string> kept;
for (auto & var : keep) {
auto s = getenv(var.c_str());
if (s) kept[var] = s;
}
clearEnv();
for (auto & var : kept)
setenv(var.first.c_str(), var.second.c_str(), 1);
} else {
if (!keep.empty())
throw UsageError("--keep does not make sense without --ignore-environment");
for (auto & var : unset)
unsetenv(var.c_str());
}
std::unordered_set<StorePath> done;
std::queue<StorePath> todo;
for (auto & path : outPaths) todo.push(path.clone());
auto unixPath = tokenizeString<Strings>(getEnv("PATH").value_or(""), ":");
while (!todo.empty()) {
auto path = todo.front().clone();
todo.pop();
if (!done.insert(path.clone()).second) continue;
if (true)
unixPath.push_front(store->printStorePath(path) + "/bin");
auto propPath = store->printStorePath(path) + "/nix-support/propagated-user-env-packages";
if (accessor->stat(propPath).type == FSAccessor::tRegular) {
for (auto & p : tokenizeString<Paths>(readFile(propPath)))
todo.push(store->parseStorePath(p));
}
}
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setenv("PATH", concatStringsSep(":", unixPath).c_str(), 1);
std::string cmd = *command.begin();
Strings args;
for (auto & arg : command) args.push_back(arg);
stopProgressBar();
restoreSignals();
restoreAffinity();
/* If this is a diverted store (i.e. its "logical" location
(typically /nix/store) differs from its "physical" location
(e.g. /home/eelco/nix/store), then run the command in a
chroot. For non-root users, this requires running it in new
mount and user namespaces. Unfortunately,
unshare(CLONE_NEWUSER) doesn't work in a multithreaded
program (which "nix" is), so we exec() a single-threaded
helper program (chrootHelper() below) to do the work. */
auto store2 = store.dynamic_pointer_cast<LocalStore>();
if (store2 && store->storeDir != store2->realStoreDir) {
Strings helperArgs = { chrootHelperName, store->storeDir, store2->realStoreDir, cmd };
for (auto & arg : args) helperArgs.push_back(arg);
execv(readLink("/proc/self/exe").c_str(), stringsToCharPtrs(helperArgs).data());
throw SysError("could not execute chroot helper");
}
execvp(cmd.c_str(), stringsToCharPtrs(args).data());
throw SysError("unable to exec '%s'", cmd);
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}
};
static auto r1 = registerCommand<CmdRun>("run");
void chrootHelper(int argc, char * * argv)
{
int p = 1;
std::string storeDir = argv[p++];
std::string realStoreDir = argv[p++];
std::string cmd = argv[p++];
Strings args;
while (p < argc)
args.push_back(argv[p++]);
#if __linux__
uid_t uid = getuid();
uid_t gid = getgid();
if (unshare(CLONE_NEWUSER | CLONE_NEWNS) == -1)
/* Try with just CLONE_NEWNS in case user namespaces are
specifically disabled. */
if (unshare(CLONE_NEWNS) == -1)
throw SysError("setting up a private mount namespace");
/* Bind-mount realStoreDir on /nix/store. If the latter mount
point doesn't already exists, we have to create a chroot
environment containing the mount point and bind mounts for the
children of /. Would be nice if we could use overlayfs here,
but that doesn't work in a user namespace yet (Ubuntu has a
patch for this:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1478578). */
if (!pathExists(storeDir)) {
// FIXME: Use overlayfs?
Path tmpDir = createTempDir();
createDirs(tmpDir + storeDir);
if (mount(realStoreDir.c_str(), (tmpDir + storeDir).c_str(), "", MS_BIND, 0) == -1)
throw SysError("mounting '%s' on '%s'", realStoreDir, storeDir);
for (auto entry : readDirectory("/")) {
auto src = "/" + entry.name;
auto st = lstat(src);
if (!S_ISDIR(st.st_mode)) continue;
Path dst = tmpDir + "/" + entry.name;
if (pathExists(dst)) continue;
if (mkdir(dst.c_str(), 0700) == -1)
throw SysError("creating directory '%s'", dst);
if (mount(src.c_str(), dst.c_str(), "", MS_BIND | MS_REC, 0) == -1)
throw SysError("mounting '%s' on '%s'", src, dst);
}
char * cwd = getcwd(0, 0);
if (!cwd) throw SysError("getting current directory");
Finally freeCwd([&]() { free(cwd); });
if (chroot(tmpDir.c_str()) == -1)
throw SysError(format("chrooting into '%s'") % tmpDir);
if (chdir(cwd) == -1)
throw SysError(format("chdir to '%s' in chroot") % cwd);
} else
if (mount(realStoreDir.c_str(), storeDir.c_str(), "", MS_BIND, 0) == -1)
throw SysError("mounting '%s' on '%s'", realStoreDir, storeDir);
writeFile("/proc/self/setgroups", "deny");
writeFile("/proc/self/uid_map", fmt("%d %d %d", uid, uid, 1));
writeFile("/proc/self/gid_map", fmt("%d %d %d", gid, gid, 1));
execvp(cmd.c_str(), stringsToCharPtrs(args).data());
throw SysError("unable to exec '%s'", cmd);
#else
throw Error("mounting the Nix store on '%s' is not supported on this platform", storeDir);
#endif
}