Differences

This shows you the differences between two versions of the page.

--- operating_systems:raspbian:raspbian [2019/04/30 14:32] – maferreira
+++ operating_systems:raspbian:raspbian [2019/07/22 09:50] (current) – removed maferreira
@@ Line 1: / Line 1: @@
-====== Raspbian ======
-===== Clone only a directory =====
-    git clone <git path>
-    cd <git directory>
-    git config core.sparsecheckout true
-    echo "<directory name>" >> .git/info/sparse-checkout
-    git checkout --
-===== Reduce time that is used to raise network interfaces =====
-As root, create the "**networking.service.d**" directory if it does not already exist and create/modify "**reduce-timeout.conf**"
-  mkdir /etc/systemd/system/networking.service.d
-  vi reduce-timeout.conf
- Then add this to your "**reduce.timeout.conf**" file
-  [Service]
-  TimeoutStartSec=XX
- <note>**XX** is the time in seconds that you want the system to wait</note>
-===== Disable swap =====
-As root, turn off the process that automatically creates a swap file
-  /etc/init.d/dphys-swapfile stop
-Also as root, add "**exit 0**" to the beginning of your "**dphys-swapfile**" file (before any executable line of code)
-  vi /etc/init.d/dphys-swapfile
-  ### BEGIN INIT INFO
-  # Provides:          dphys-swapfile
-  # Required-Start:    $syslog $remote_fs
-  # Required-Stop:     $syslog $remote_fs
-  # Should-Start:      $local_fs
-  # Should-Stop:       $local_fs
-  # Default-Start:     2 3 4 5
-  # Default-Stop:
-  # Short-Description: Autogenerate and use a swap file
-  # Description:       This init.d script exists so one does not need to have a fixed size
-  #                    swap partition. Instead install without swap partition and then run
-  #                    this, with file size (re-)computed automatically to fit the current
-  #                    RAM size.
-  ### END INIT INFO
-  exit 0
-  . /lib/lsb/init-functions
-  # get ready to work
-  PATH=/sbin:/bin:/usr/sbin:/usr/bin
-  export PATH
-  ...
-===== Stop process using files in / =====
-First we need to know which processes are using files in the directory we want to make read-only. To do so,  you can use the fuser command.
-  sudo fuser -v -m /
-You should have something like this
-    USER        PID ACCESS COMMAND
-  /:                   root     kernel mount /
-  Some other process
-  root        423 Frce. rsyslogd
-  root        657 Frce. dhclient
-  Some other process
- <note>I only choose these 2 process because they are the only ones writing into files (According to the fuser man page F stands for "open file for writing").</note>
-Now, if you check rsyslog status it might be stopped because it uses /var/spool/rsyslog, and /var/spool is mounted in tmpfs. This means that the directory used by rsyslog is not created/available at boot. To solve this problem you need a script that is executed at startup. To do so, create a systemd unit file.
-    vim /etc/systemd/system/generateRsyslogStructure.service
-    [Unit]
-    Description=Generate rsyslog structure
-    Before=rsyslog.service
-    [Service]
-    ExecStart=/home/acdsn/git/acdsn-scripts/PI/generateRsyslogStructure.sh
-    Type=oneshot
-    [Install]
-    WantedBy=default.target
-And then create "**createSyslogDir.sh**"
-    #!/bin/bash
-    if [ -r /etc/rsyslog.conf ]; then
-        WorkDirectory=$(grep "WorkDirectory" /etc/rsyslog.conf | cut -d\  -f2)
-    else
-        echo "Cannot read /etc/rsyslog.conf" >> /tmp/rsyslogService.txt
-        exit 1
-    fi
-    [ -d "$WorkDirectory" ] || mkdir $WorkDirectory
-    exit 0
-Restart rsyslog and it should work!
-From the 2 processes I showed you earlier, only dhclient remains.
-dhclient is launched by dhcpcd which uses a file as database for each network interface (/var/lib/dhcpcd5/dhcpcd-<network interface name>.lease). As a database, this file is written and read often. We need to move  the lease file to a read-only directory (in our case it can be /tmp).
-After reading the dhcpcd documentation, I only found a -lf option to specify the path to the lease files. But that is not the best solution since the configuration is only used in runtime. It would be better if there was an option in the config file where I could specify the lease files path.
-So I took a look to the dhcpcd.conf manual page but I didn't found a "leasefile path" option. I also research in Internet if there was a "leasefile path", but again, no results.
-I started thinking if I couldn't see the option from the documentation I would have to analyze the source code.
-If you have done the BLFS project before, you might remember installing dhcpcd package.
-Here is what they used to compile it:
-  ./configure --libexecdir=/lib/dhcpcd \
-              --dbdir=/var/lib/dhcpcd  &&
-  make
-  sudo make install
-As you can see, dbdir is a compilation variable that contains the path where dhcpcd can find the lease files for each network interface.
-Here is the precedure I used to try to find if there is a config file other than dhcpcd.conf or if there is an option to change the default lease files path.
-  - Find out where dbdir is defined/used
-  - Search for some kind of read_config function and see where it is used
-Unfortunately, this method didn't work and I had to use a different one.
-I searched in the dhcpcd.conf manual page for an option that isn't used very often in order to make the "debug" process easy.
-I choose the **xidhwaddr** option. I executed **grep -r -i "xidhwaddr" .** in the dhcpcd-6.10.1 directory and I had the following result:
-  ./dhcpcd.8.in:.It Fl H , Fl Fl xidhwaddr
-  ./dhcpcd.conf.5.in:.It Ic xidhwaddr
-  ./if-options.c:	{"xidhwaddr",       no_argument,       NULL, 'H'},
-After this, I took a look to the if-options.c file to know where this C struct option where used. The first line of code I found contained a **parse_config_line function** which had a **char *line** parameter.
-The next step was to find out where this function was called. I found out that it was called by a read_config function which didn't have a char *line parameter.
-It was obvious that the line variable was initialised and declared inside read_config. After a research in that function, I realised that the line variable contained data from either dhcpcd.conf or /lib/dhcpcd/dhcpcd-definitions.conf (an embedded config file).
-After some time of lecture, I found out that there wasn't a config file with a lease-file option.
-  * [[Clean installation]]
-  * [[Minimal configuration]]
-  * [[Tricks]]