Tag Archives: linux

Hardware, OS

Installing Linux Mint 18.3 with NVIDIA GTX 1070

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I became very frustrated when trying to install the latest Linux Mint on my desktop, which contains an NVIDIA GTX 1070 graphics card. No matter what I tried I couldn’t even get the live CD environment to show up. It would stay at text, and even play the login sound, but no matter what I pressed I couldn’t get anything to come up on the display.

After much digging I came across an Ubuntu forum post which directed me to this manual describing different boot-time options. I had read somewhere that you want nomodeset to be enabled, but that didn’t cut it. Finally after reading the Ubuntu options I found the second half – vga=791

So, to install (and run for the first time before installing NVIDIA drivers) Linux Mint on a machine that has an NVIDIA Geforce GTX 1070, you have to edit the grub startup options (by pressing esc / tab) and append the following to the kernel line:

nomodeset vga=791

Also, if you manually partition the installation, make sure that the /boot partition is EXT2. I had first installed it as EXT4 but ran into strange problems.. restarting and making it EXT2 made those problems go away.

OS

Nextcloud External Files SMB not working – Empty Response from Server

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I beat my head against the wall for hours trying to figure out why external storage wasn’t working with my Nextcloud instance after I migrated it over to CentOS 7. All I kept getting was a very unhelpful

There was an error with message: Empty response from the server.

I installed all the libraries multiple times. I tried different versions of smbclient and php-smbclient but the error kept happening! Eventually I decided to check the samba logs of my samba server. Sure enough:

 create_connection_session_info failed: NT_STATUS_ACCESS_DENIED

The username and password I was using was correct. I read on some forum (sorry, no link) to put something in the Workgroup field. Voila! As soon as I populated the workgroup field in Nextcloud for my SMB shares, they all worked!

CLI

MariaDB with Active Directory authentication via PAM module

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I needed to get mariadb authenticating users via Active Directory at work. Configuration was confusing until I stumbled across this article saying you can just tie into the system’s PAM configuration., which in my case is already configured for AD authentication. Awesome!

First, enable PAM plugin and restart mariadb:

/etc/my.cnf, anywhere in the mysqld section

plugin-load=auth_pam.so

Restart mariadb:

sudo systemctl restart mariadb

Next, configure a PAM file to interface with mariadb:

sudo vi /etc/pam.d/mysql
auth include system-auth 
account required pam_nologin.so 
account include system-auth 
password include system-auth 
session optional pam_keyinit.so force revoke 
session include system-auth 
session required pam_loginuid.so

Create catch all user in MariaDB and configure to use your PAM configuration:

CREATE USER ''@'%' IDENTIFIED VIA pam USING 'mysql';

Lastly, grant permissions in mariadb being sure to specify pam as the mechanism:

GRANT ALL PRIVILEGES on <database>.* to '<user>'@'<host>' IDENTIFIED VIA pam;

Profit.

Update 4-23-2019

You can use the pam_user_map module to grant permission to AD groups. This allows using Active Directory groups to completely manage permissions instead of creating users manually in the database. The procedure is outlined here.

Compile & Install pam_user_map module

sudo yum -y install gcc pam-devel  
wget https://raw.githubusercontent.com/MariaDB/server/10.4/plugin/auth_pam/mapper/pam_user_map.c 
gcc pam_user_map.c -shared -lpam -fPIC -o pam_user_map.so 
sudo install --mode=0755 pam_user_map.so /lib64/security/

Create mysql user and grant it permissions you would like your group to have

CREATE USER '<DBUSER>'@'%' IDENTIFIED BY 'strongpassword';
GRANT ALL PRIVILEGES ON *.* TO '<DBUSER>'@'%' ;

CREATE USER ''@'%' IDENTIFIED VIA pam USING 'mariadb';
GRANT PROXY ON '<DBUSER>'@'%' TO ''@'%';

Configure pam_user_map user/group mappings by creating /etc/security/user_map.conf and add with group mappings. Note pam_user_map doesn’t tolerate special characters, such as the carat sign, which powerbroker uses to indicate spaces. I ended up just renaming the group to not have any spaces in it.

#/etc/security/user_map.conf  
@orig_pam_group_name: mapped_mariadb_user_name

Configure PAM to include pam_user_map.so as the last step in the process. Note the process I uploaded earlier doesn’t work well with groups, so here is my new process (I’m using Powerbroker Open for AD mapping)

auth        required      pam_lsass.so      try_first_pass
auth required pam_user_map.so debug
account required pam_permit.so

Note I’ve also included pam_permit.so so I didn’t need to create AD groups to match what I’ve configured in user_map.conf above.

CLI

Rename files to reflect modified time while preserving extension

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I’m undergoing a big project of scanning old family scrapbooks. I have two scanners involved, each with their own naming scheme, dumping files of various types (pdf, jpg) into the same folder. I need to have an accurate chronological view of when things were scanned (nothing was scanned at the exact same moment.) At this point the only way to get this information is to sort all the files by modified time,  but no other programs but a file manager look at files this way. I needed a way to rename all the files to reflect their modified time.

I found a couple different ways to do this, but settled on a bash for loop utilizing the stat, sed, and mv commands.

Challenge 1

Capture the extension of the files.

Using sed:

ls <filename> | sed 's/.*\(\..*\)$/\1/'

Challenge 2

Obtain the modified time of your file in an acceptable format. I do this using the stat command.

stat -c %y <filename>

%y is the best option here – it leaves no room for ambiguity. You could also choose %Y so the filenames aren’t so large and don’t contain colons (some systems struggle with this.) The downside do this is you only have to-the-second precision. In my case I had a few files that had the same epoch timestamp, which caused problems. More on how to format this can be found here and here.

Stringing it all together

I wrapped it all up in a bash for loop with appropriate variables. This was my final command, which I ran inside the directory I wanted to modify:

for file in *; do name=$(stat -c %y "$file"); ext=$(echo "$file" | sed 's/.*\(\..*\)$/\1/'); mv -n "$file" "$name$ext"; done

The for loop goes through each file one at a time and assigns it to the $file variable.  I then create the name variable which uses the stat command to obtain a precise date modified timestamp of the file. The ext variable is derived from the filename but only keeps the extension (using sed.) The last step uses mv -n (no clobber mode – don’t overwrite anything) to rename the original file to its date modified timestamp. The result: a directory where each file is named precisely when it was modified – a true chronology of what was scanned irrespective of file extension or which scanner created the file. Success.

CLI, OS, Web

Make Java run on privileged ports in CentOS 7

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I recently gnashed my teeth at trying to get java to directly bind to port 443 instead of using nginx to proxy to a java application I had to use. I was surprised at the complication of finding the solution, but I eventually did thanks to the following sites:

https://superuser.com/questions/710253/allow-non-root-process-to-bind-to-port-80-and-443/892391

https://github.com/kaitoy/pcap4j/issues/63

First, determine the full path of your current java install:

sudo update-alternatives --config java

In my CentOS 7 install, the java binary was located here:

/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.151-1.b12.el7_4.x86_64/jre/bin/java

Next, use setcap to configure java to be able to bind to port 443:

sudo setcap CAP_NET_BIND_SERVICE=+eip /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.151-1.b12.el7_4.x86_64/jre/bin/java

Now, test to make sure java works:

java -version

java: error while loading shared libraries: libjli.so: cannot open shared object file: No such file or directory

The above error means that after setting setcap, it breaks how java looks for its library to run. To fix this, we need to symlink the library it’s looking for into /usr/lib, then run ldconfig

sudo ln -s /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.151-1.b12.el7_4.x86_64/jre/lib/amd64/jli/libjli.so /usr/lib/
sudo ldconfig

Now test Java again:

java -version

It took longer than I like to admit to get this working, but it it does indeed work this way.

Web

Whitelist IPs with varnish

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I recently needed to restrict which IP addresses can access wp-login.php for a wordpress site of mine. This site is sitting behind varnish cache for speed. Modifying htaccess doesn’t work in this case so I have to modify the varnish configuration in order to get this to work.

The varnish documentation is actually quite good at telling you what you need to do.  You have to first specify an acl and then in the vcl_recv function specify the action when these IPs are used.

I kept running into a problem where varnish wouldn’t compile. I kept receiving this error:

"Expected CSTR got 'admin_net'" (C String?)

It turns out my load balancer does not support the PROXY protocol, so client.ip is always the IP of the load balancer, not the IP of the person making the request.

The solution was finally found here where it was explained that in absence of PROXY protocol you can use the std.ip() function to convert a string containing an IP address to the value varnish expects an IP address to be, in order to check it against an ACL (see here for syntax reference.)

I then had to take it a step further to trim all the extraneous commas and quotes from X-Forwarded-For so that the std.ip() function would work:

# set realIP by trimming CloudFlare IP which will be used for various checks
set req.http.X-Actual-IP = regsub(req.http.X-Forwarded-For, "[, ].*$", "");

With these three bits combined I was able to properly restrict access to wp-login.php to a specified whitelist of IP addresses:

acl admin {
 "10.0.0.0/24";
 "10.0.1.0/24";
 "10.0.2.0/24";
}

...

sub vcl_recv {
...

 # set realIP by trimming CloudFlare IP which will be used for various checks
 set req.http.X-Actual-IP = regsub(req.http.X-Forwarded-For, "[, ].*$", "");

 #Deny wp-login.php access if not in admin ACL
 if ((std.ip(req.http.X-Actual-IP, "0.0.0.0") !~ admin) && req.url ~ "^/wp-login.php") {
  return(synth(403, "Access denied."));
 }
...
}

Success.

CLI, OS

gvfs-mount doesn’t use kerberos ticket fix

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I had a very frustrating issue when I switched my work desktop from Linux Mint to CentOS 7. My network drives no longer would mount using a kerberos ticket. Before, when I would initialize a kerberos ticket I could mount network shares without any kind of username or password prompt:

kinit
gvfs-mount smb://server/share

With CentOS 7, though, the above process would produce a username and password prompt. After much searching I came across this forum that contained the answer: append your fully qualified domain name to the server. Now the process is like this:

kinit
gvfs-mount smb://server.full.fqdn.name/share

and it worked!

CLI, OS

Fix no bluetooth devices found in Linux Mint

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I had a peculiar issue today where I suddenly lost the ability to see any bluetooth devices on my Linux Mint 18.2 desktop utilizing a Plugable USB Bluetooth adapter.

The fix involved checking kernel messages for anything insightful. In my case this is what led me to the solution:

[ 608.988353] Bluetooth: hci0: BCM: Patch brcm/BCM20702A1-0a5c-21e8.hcd not found
[ 609.156320] Bluetooth: hci0: BCM: chip id 63
[ 609.172330] Bluetooth: hci0: LPP-3389-WIN
[ 609.173313] Bluetooth: hci0: BCM20702A1 (001.002.014) build 1764
[ 609.173347] bluetooth hci0: Direct firmware load for brcm/BCM20702A1-0a5c-21e8.hcd failed with error -2

After some googling I finally came across the solution here. The fix is to download the firmware for your bluetooth adapter and place it in the place the bluetooth kernel module expects it to be in, then to reload the bluetooth kernel module.

sudo mkdir -p /lib/firmware/brcm
sudo wget https://s3.amazonaws.com/plugable/bin/fw-0a5c_21e8.hcd -O /lib/firmware/brcm/BCM20702A1-0a5c-21e8.hcd
sudo rmmod btusb bnep bluetooth btrtl btintel bnep btbcm
sudo modprobe btusb bnep bluetooth btrtl btintel bnep btbcm

That did the trick! You can also reboot your machine instead of removing / re-loading the kernel modules and it will accomplish the same thing.

CLI, Web

Fix WordPress “Sorry, you are not allowed to access this page.”

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I recently came across an issue with my WordPress installation. It’s situated behind a load balancer where SSL is terminated. The load balancer takes HTTPS traffic, then forwards it as HTTP on port 80 to the wordpress server.

I was running issues with a redirect loop after installing wordpress. The solution was to add this bit of code to wp-config.php:

define('FORCE_SSL_ADMIN', true);
if ($_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https')
 $_SERVER['HTTPS']='on';

This solves the redirect loop issue but then I ran into a different problem. When I tried to sign into wp-admin I would get this message:

Sorry, you are not allowed to access this page.

After much digging I found this post which emphasizes that you must place that code BEFORE anything else in wp-config.php (except for the beginning PHP tag.) Success!