Category Archives: linux

GDM fails to start

Experimenting with VMs on Ubuntu, I had the system running on a relatively small root disk. Was troubleshooting problems in the disk array, doing a lot of booting, and crashing, when suddenly the boot wouldn’t finish. Fortunately the boot wasn’t quiet and I could watch as it tried 20-30 times to start the gdm service.

I change the default to multi-user.target and got it up, and what do you know, the root filesystem is at 100%. Cleaned up some logs and crash logs and it came right up.

Interesting that it doesn’t have a way to at least alert you that is what its problem is.

Laptop backup and Lid events

I have some scripts which try to do backups on the laptop. It is a little more involved, since the laptop lid is closed most of the time, including at night. So the strategy is to have a cron job start periodically, determine if a backup had been done today and if not, attempt to do one.

Since the laptop could be in various locations, it tries to determine where it is – i.e. if it is in a known location (my house or my sister’s house, or one of my DC friends houses). If so, it can back up accordingly. This is done using SSIDs, which is adequate if not elegant.

One issue I’ve had is if the attempted backup starts right after the lid is opened, the wireless may not be ready yet, and so the backup may fail on account of no network. So I set out to try to figure out how to detect when the network is available, so the script can obtain that information. Continue reading Laptop backup and Lid events

Clamav and Amavisd

I find the whole clamav subsystem to be fragile. I think this is because it is written as a tool which stands on its own, but I’m only using it as a subsystem hung onto the side of amavisd. So there is some hand-waving and jiggery pokery with the sockets and the permissions to enable the two to communicate, which has to be done manually, and is not properly a part of either subsystem.

I have another article on setting up this subsystem here, which records some of the stuff being done. I think basically, amavisd has to know where the shared socket is, in order to send messages to clamav to check, and they have to agree on the ownership and permissions of the socket and its directory.

Once in a while that stuff gets crosswise, and since I only vaguely understood what was going on, and only did the hand-waving by rote, I got annoyed with it. I’ve grown used to being able to just have things slot in and work, without my having to actually dig in and understand them. The nerve of these people, to expect me to know what is going on in order to make it work! Irony intended. Continue reading Clamav and Amavisd

Recording last authentication

I wanted a way to be able to determine roughly how long it had been since a user had been active. I defined active to mean that the user had had to authenticate onto a system. This is so that a box on which the user had logged in has gone into screen lock, and the user has then authenticated again to the display manager.

I used the audit log of auditd to detect when a user has authenticated to a display manager. Auditd comes installed on Fedora, but I had to install it on the ubuntu boxes. Continue reading Recording last authentication

SVN Error E175002

I have been plagued by this error in subversion particularly when trying to commit from some of the boxes which I use less frequently:

svn: E175002: Unexpected HTTP status 200 ‘OK’ on ‘POST’ request to ‘/svn/!svn/me’

I have spent hours doing searches, reading posts, but have never found anyone whose issue was exactly like mine, not been able to figure it out based on other peoples issues. I resolved today to pay serious attention to figuring it out.

The solution turned out to be related to the url I used when I check something out of the svn repository. Long ago I set up a cname in dns for svn.wmbuck.net, and for a long time I used it. There is an apache config file for the servername svn.wmbuck.net, and it redirects http to https. Then at some point I began to just use https://wmbuck.net/svn/… to check things out. And that is where I went wrong, because that will work fine to do checkout, but when I try to commit from a box with that url (wmbuck.net) the http request is being routed to the default server, and the setup of the SSL session is failing.

I’m unsure exactly what is happening to cause the request to go to the default server. Perhaps the commit request does not specify SNI information.

What I do know is how to fix it. Do the checkout with https://svn.wmbuck.net/svn/ and commits work fine.

Running Apache under my username

I had some trouble on the development box with permissions and decided it would be “easy” to just have apache run under user dee, that would just make everything so much easier. Right.

Two things have come up so far, and more likely to follow. One, I had to change the ownership on /var/lib/php/session from apache to dee. Second, I had to add dee into tlsusers so the media stuff can read the certificate.

This may have been a bad idea.

1/31/18: Went back to using apache user, when I moved to Fedora 27. Fedora now uses php-fpm service, and now apache needs to open a socket to it, and it just became complicated.

4K Screen

I’ve been using this Samsung 4K screen for 3 years. I never adjusted any of the parameters for making things larger. I just got used to the small fonts, and blew things up by application when I needed to.

I’ve been doing some reading in anticipation of getting a new laptop maybe with hidpi. Learned stuff about changing resolution.

With Gnome-Tweak tool->Windows->HIDPI Window scaling, can blow up everything in Gnome. Can only have integer values, so with 2, I can double the size. But after several years of smaller sizes I don’t really like this. Might need it on the laptop though.

With Firefox and Thunderbird, use config editor and find layout.css.devPixelsPerPx. This can have non integer values and 1.5 in Thunderbird is better for me. For Firefox I currently have it set at 1.3.
Continue reading 4K Screen

Apache module debugging

I have some problem using mod_xsendfile on tarragon. I’ve been working on getting this working for 2 days. I have had to get into the source code of the apache module to figure it out, and I want to turn on the debugging option to see what is going on.

So I have to recompile the c source file, with the define of _DEBUG, and install the it as a module. Had to figure out how to do this. It is very easy. But easy doesn’t mean I’ll remember it, thus this post.

I cloned the source:

git clone https://github.com/nmaier/mod_xsendfile (into my local git repo), and then cd into the directory, and

apxs -D_DEBUG -i -c mod_xsendfile.c

This creates the module with debugging defined, and puts it in /usr/lib64/httpd/modules/mod_xsendfile.so

It still needs to be loaded into apache. Instructions at his site say to use the -a flag, to activate, but while that would work on a simple site, it tries to put the LoadModule into /etc/httpd/conf/httpd.conf, and all my LoadModule statements are in files in the directory /etc/httpd/conf.modules.d so I need to create /etc/httpd/conf.modules.d/xsendfile.conf containing:

LoadModule xsendfile_module modules/mod_xsendfile.so

The module will log debug statements, but this still won’t actually get you any log records until you set LogLevel debug in the apache config file.

Then restart apache and Bob’s your uncle.

Adjusting the size of the tarragondata volume

At one point I was getting low on space on tarragondata, so I added an additional physical device to the btrfs filesystem containing tarragondata.

[root@tarragon backup_scripts]# btrfs fi show
Label: 'tarragon_data' uuid: d6e4b6fc-8745-4e6e-b6b4-8548142b5154
 Total devices 2 FS bytes used 92.04GiB
 devid 1 size 120.00GiB used 120.00GiB path /dev/xvdf1
 devid 2 size 30.00GiB used 30.00GiB path /dev/xvdg

This is fine, but there are a couple of problems. The main one is that I can no longer use the EC2 snapshot capability on tarragondata, which meant that the nightly EC2 snapshot feature I was using had to be deimplemented.

But now I am about to create a new tarragon instance, and it would be really helpful to be able to snapshot tarragondata (Amazon snapshot, not btrfs snapshot) and then create a new Amazon volume with a consistent snapshot for testing. Continue reading Adjusting the size of the tarragondata volume

mdadm consistency checks

On ubuntu it seems there is an automatic mdadm array check provided in /etc/cron.d/mdadm, automatically installed with mdadm. This invokes a utility /usr/share/mdadm/checkarray and the cron is set to run this on the first Sunday of every month at 12:57am. And it is set to do this check on all arrays at one time.

This is horrible! So with 5 arrays, totalling 25TB, when this sucker fires up it quickly saturates the i/o capacity of cinnamon, slows to a crawl and settles in to run forever.

I’ve commented that out, and added my own /etc/cron.d/dee_mdadm which doesn’t do all the goofy shenanigans to try to ensure the thing runs on a Sunday (WHY?! Because the guy who wrote it doesn’t work on Sunday?). Instead, my version simply runs on the first of the month, at 12:57am, and on each month it starts the consistency check on a different array. I have 5 arrays, so 3 are checked twice a year, and 2 are checked thrice. Checking just one at a time means there is a good chance it will be done before morning, at least for the small arrays.

I don’t really think the whole consistency check idea is doing me much good, but at least this doesn’t unaccountably bring the system to its knees on the first Sunday of every month.