-<p>For some years now, I have wondered how we should handle laptops in
-Debian Edu. The Debian Edu infrastructure is mostly designed to
-handle stationary computers, and less suited for computers that come
-and go.</p>
-
-<p>Now I finally believe I have an sensible idea on how to adjust
-Debian Edu for laptops, by introducing a new profile for them, for
-example called Roaming Workstations. Here are my thought on this.
-The setup would consist of the following:</p>
-
-<ul>
-
- <li>During installation, the user name of the owner / primary user of
- the laptop is requested and a local home directory is set up for
- the user, with uid and gid information fetched from the LDAP
- server. This allow the user to work also when offline. The
- central home directory can be available in a subdirectory on
- request, for example mounted via CIFS. It could be mounted
- automatically when a user log in while on the Debian Edu network,
- and unmounted when the machine is taken away (network down,
- hibernate, etc), it can be set up to do automatic mounting on
- request (using autofs), or perhaps some GUI button on the desktop
- can be used to access it when needed. Perhaps it is enough to use
- the fish protocol in KDE?</li>
-
- <li>Password checking is set up to use LDAP or Kerberos
- authentication when the machine is on the Debian Edu network, and
- to cache the password for offline checking when the machine unable
- to reach the LDAP or Kerberos server. This can be done using
- <a href="http://www.padl.com/OSS/pam_ccreds.html">libpam-ccreds</a>
- or the Fedora developed
- <a href="https://fedoraproject.org/wiki/Features/SSSD">System
- Security Services Daemon</a> packages.</li>
-
- <li>File synchronisation with the central home directory is set up
- using a shared directory in both the local and the central home
- directory, using unison.</li>
-
- <li>Printing should be set up to print to all printers broadcasting
- their existence on the local network, and should then work out of
- the box with CUPS. For sites needing accurate printer quotas, some
- system with Kerberos authentication or printing via ssh could be
- implemented.</li>
-
- <li>For users that should have local root access to their laptop,
- sudo should be used to allow this to the local user.</li>
-
- <li>It would be nice if user and group information from LDAP is
- cached on the client, but given that there are entries for the
- local user and primary group in /etc/, it should not be needed.</li>
-
-</ul>
-
-<p>I believe all the pieces to implement this are in Debian/testing at
-the moment. If we work quickly, we should be able to get this ready
-in time for the Squeeze release to freeze. Some of the pieces need
-tweaking, like libpam-ccreds should get support for pam-auth-update
-(<a href="http://bugs.debian.org/566718">#566718</a>) and nslcd (or
-perhaps debian-edu-config) should get some integration code to stop
-its daemon when the LDAP server is unavailable to avoid long timeouts
-when disconnected from the net. If we get Kerberos enabled, we need
-to make sure we avoid long timeouts there too.</p>
-
-<p>If you want to help out with implementing this for Debian Edu,
-please contact us on debian-edu@lists.debian.org.</p>
+<p>A few years ago, I was involved in a project planning to use
+Windows file servers as home directory servers for Debian
+Edu/Skolelinux machines. This was thought to be no problem, as the
+access would be through the SMB network file system protocol, and we
+knew other sites used SMB with unix and samba as the file server to
+mount home directories without any problems. But, after months of
+struggling, we had to conclude that our goal was impossible.</p>
+
+<p>The reason is simply that while SMB can be used for home
+directories when the file server is Samba running on Unix, this only
+work because of Samba have some extensions and the fact that the
+underlying file system is a unix file system. When using a Windows
+file server, the underlying file system do not have POSIX semantics,
+and several programs will fail if the users home directory where they
+want to store their configuration lack POSIX semantics.</p>
+
+<p>As part of this work, I wrote a small C program I want to share
+with you all, to replicate a few of the problematic applications (like
+OpenOffice.org and GCompris) and see if the file system was working as
+it should. If you find yourself in spooky file system land, it might
+help you find your way out again. This is the fs-test.c source:</p>
+
+<pre>
+/*
+ * Some tests to check the file system sematics. Used to verify that
+ * CIFS from a windows server do not work properly as a linux home
+ * directory.
+ * License: GPL v2 or later
+ *
+ * needs libsqlite3-dev and build-essential installed
+ * compile with: gcc -Wall -lsqlite3 -DTEST_SQLITE fs-test.c -o fs-test
+*/
+
+#define _FILE_OFFSET_BITS 64
+#define _LARGEFILE_SOURCE 1
+#define _LARGEFILE64_SOURCE 1
+
+#define _GNU_SOURCE /* for asprintf() */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#ifdef TEST_SQLITE
+/*
+ * Test sqlite open, as done by gcompris require the libsqlite3-dev
+ * package and linking with -lsqlite3. A more low level test is
+ * below.
+ * See also <URL: http://www.sqlite.org./faq.html#q5 >.
+ */
+#include <sqlite3.h>
+#define CREATE_TABLE_USERS \
+ "CREATE TABLE users (user_id INT UNIQUE, login TEXT, lastname TEXT, firstname TEXT, birthdate TEXT, class_id INT ); "
+int test_sqlite_open(void) {
+ char *zErrMsg;
+ char *name = "testsqlite.db";
+ sqlite3 *db=NULL;
+ unlink(name);
+ int rc = sqlite3_open(name, &db);
+ if( rc ){
+ printf("error: sqlite open of %s failed: %s\n", name, sqlite3_errmsg(db));
+ sqlite3_close(db);
+ return -1;
+ }
+
+ /* create tables */
+ rc = sqlite3_exec(db,CREATE_TABLE_USERS, NULL, 0, &zErrMsg);
+ if( rc != SQLITE_OK ){
+ printf("error: sqlite table create failed: %s\n", zErrMsg);
+ sqlite3_close(db);
+ return -1;
+ }
+ printf("info: sqlite worked\n");
+ sqlite3_close(db);
+ return 0;
+}
+#endif /* TEST_SQLITE */
+
+/*
+ * Demonstrate locking issue found in gcompris using sqlite3. This
+ * work with ext3, but not with cifs server on Windows 2003. This is
+ * done in the sqlite3 library.
+ * See also
+ * <URL:http://www.cygwin.com/ml/cygwin/2001-08/msg00854.html> and the
+ * POSIX specification
+ * <URL:http://www.opengroup.org/onlinepubs/009695399/functions/fcntl.html>.
+ */
+int test_gcompris_locking(void) {
+ struct flock fl;
+ char *name = "testsqlite.db";
+ unlink(name);
+ int fd = open(name, O_RDWR|O_CREAT|O_LARGEFILE, 0644);
+ printf("info: testing fcntl locking\n");
+
+ fl.l_whence = SEEK_SET;
+ fl.l_pid = getpid();
+ printf(" Read-locking 1 byte from 1073741824");
+ fl.l_start = 1073741824;
+ fl.l_len = 1;
+ fl.l_type = F_RDLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Read-locking 510 byte from 1073741826");
+ fl.l_start = 1073741826;
+ fl.l_len = 510;
+ fl.l_type = F_RDLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Unlocking 1 byte from 1073741824");
+ fl.l_start = 1073741824;
+ fl.l_len = 1;
+ fl.l_type = F_UNLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Write-locking 1 byte from 1073741824");
+ fl.l_start = 1073741824;
+ fl.l_len = 1;
+ fl.l_type = F_WRLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Write-locking 510 byte from 1073741826");
+ fl.l_start = 1073741826;
+ fl.l_len = 510;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ printf(" Unlocking 2 byte from 1073741824");
+ fl.l_start = 1073741824;
+ fl.l_len = 2;
+ fl.l_type = F_UNLCK;
+ if (0 != fcntl(fd, F_SETLK, &fl) ) printf(" - error!\n"); else printf("\n");
+
+ close(fd);
+ return 0;
+}
+
+/*
+ * Test if permissions of freshly created directories allow entries
+ * below them. This was a problem with OpenOffice.org and gcompris.
+ * Mounting with option 'sync' seem to solve this problem while
+ * slowing down file operations.
+ */
+int test_subdirectory_creation(void) {
+#define LEVELS 5
+ char *path = strdup("test");
+ char *dirs[LEVELS];
+ int level;
+ printf("info: testing subdirectory creation\n");
+ for (level = 0; level < LEVELS; level++) {
+ char *newpath = NULL;
+ if (-1 == mkdir(path, 0777)) {
+ printf(" error: Unable to create directory '%s': %s\n",
+ path, strerror(errno));
+ break;
+ }
+ asprintf(&newpath, "%s/%s", path, "test");
+ free(path);
+ path = newpath;
+ }
+ return 0;
+}
+
+/*
+ * Test if symlinks can be created. This was a problem detected with
+ * KDE.
+ */
+int test_symlinks(void) {
+ printf("info: testing symlink creation\n");
+ unlink("symlink");
+ if (-1 == symlink("file", "symlink"))
+ printf(" error: Unable to create symlink\n");
+ return 0;
+}
+
+int main(int argc, char **argv) {
+ printf("Testing POSIX/Unix sematics on file system\n");
+ test_symlinks();
+ test_subdirectory_creation();
+#ifdef TEST_SQLITE
+ test_sqlite_open();
+#endif /* TEST_SQLITE */
+ test_gcompris_locking();
+ return 0;
+}
+</pre>
+
+<p>When everything is working, it should print something like
+this:</p>
+
+<pre>
+Testing POSIX/Unix sematics on file system
+info: testing symlink creation
+info: testing subdirectory creation
+info: sqlite worked
+info: testing fcntl locking
+ Read-locking 1 byte from 1073741824
+ Read-locking 510 byte from 1073741826
+ Unlocking 1 byte from 1073741824
+ Write-locking 1 byte from 1073741824
+ Write-locking 510 byte from 1073741826
+ Unlocking 2 byte from 1073741824
+</pre>
+
+<p>I do not remember the exact details of the problems we saw, but one
+of them was with locking, where if I remember correctly, POSIX allow a
+read-only lock to be upgraded to a read-write lock without unlocking
+the read-only lock (while Windows do not). Another was a bug in the
+CIFS/SMB client implementation in the Linux kernel where directory
+meta information would be wrong for a fraction of a second, making
+OpenOffice.org fail to create its deep directory tree because it was
+not allowed to create files in its freshly created directory.</p>
+
+<p>Anyway, here is a nice tool for your tool box, might you never need
+it. :)</p>
projects / homepage.git / blobdiff