SysAdminStuff

Linux and windows cofigurations snippets

Linux

Mount a `LVM` in linux.

Connect the drive
run the command lvm
- Inside the lvm terminal
- pvscan <- (note the PV name)
- lvscan <- (note the LV names)
- lvchange -ay /dev/{pv-name-here} eg lvchange -ay /dev/fedora_a/home
Now mount the dive with that name: sudo mount /dev/fedora_a/home /tmp/fed24/
Here the drive is ready for use in /tmp/fed24

To remove the disk:

umount /mnt
lvm
- lvchange -an /dev/{pv-name-here}

Max partitions for MMC

The linux kernel defines the number of partitios per MMC block device to be CONFIG_MMC_BLOCK_MINORS. This defines the number of minors per block device. One is needed for every partition on the disk, plus one for the whole disk. Number of total MMC minors is 256, so your number of supported block devices will be limited by 256 divided by CONFIG_MMC_BLOCK_MINORS. Default is 8 to be backwards compatible with previous hardwired device numbering.

src

Commands:

pvs: pvs — report information about physical volumes

lvdisplay: lvdisplay — display attributes of a logical volume

To mount use the regular procedure:

Create a directory mkdir HD_Laptopo
Mount as a regular partion mount mount /dev/vg_<host>/lv_home ./HD_Laptopo

Command line open image from console for gnome:

eog <path to image>

Get disply settings in console:

xdpyinfo

Get the display size: xdpyinfo | grep dim

Call the configured service to open a specific file:

`xdg-open

Windows:

Change the prompt in cmd

prompt $$

Go to sleep:

rundll32.exe powrprof.dll,SetSuspendState 0,1,0

Share a location:

net share <share_name>=<full path> /GRANT:<user>,[READ | CHANGE | FULL]

Look what is being shared:

net share

Discover connected devices in the network

ping 192.168.1.255
arp -n

add user to sudoers grp

sudo usermod -a -G sudo <user>

Create and user

Use adduser, its a front end for the more low-level useradd. adduser creates the $HOME for the in-creation user, while useradd does not.

Encrypt files in device

https://www.veracrypt.fr/en/Home.html

Find strings in files

For Windows

findstr /spin /c:"find in text" [files]

s: recursive
p: skip non-printable chars
i: case insensitive
n: Print line numbers
/c:: String to look up
[files]: a regex for the file name e.g.: c_*.h

For linux

grep -Riln 'Text to find' /<path>

Chain grep

Instead of chainig grep calls with pipes, use the next option.

grep -v -e <regexa> -e <regexb> -e <regexc> -e <regexd>...

Other option is to enable the flag -E.

grep -Ev '(regexa|regexb|regexc|...)'

Or use a file which contains all the patters, one per line.

grep -v -f patterns.txt

grep -rnw '/path/to/somewhere/' -e 'pattern'

-r or -R is recursive,
-n is line number, and
-w stands for match the whole word.
-l (lower-case L) can be added to just give the file name of matching files.

Along with these, --exclude, --include, --exclude-dir flags could be used for efficient searching:

This will only search through those files which have .c or .h extensions:

grep --include=\*.{c,h} -rnw '/path/to/somewhere/' -e "pattern"

This will exclude searching all the files ending with .o extension:

grep --exclude=*.o -rnw '/path/to/somewhere/' -e "pattern"

For directories it's possible to exclude a particular directory(ies) through --exclude-dir parameter. For example, this will exclude the dirs dir1/, dir2/ and all of them matching *.dst/:

grep --exclude-dir={dir1,dir2,*.dst} -rnw '/path/to/somewhere/' -e "pattern"

Execute command on a file matching pattern

find -name "*.swp" - exec rm {} ';' # The command must be terminated with ';' or '\;'

Complicated way to write files when there's no editor.

$ cat > filename.txt
write stuff
other stuff
and so on
^D

Done

`setuid` and `setgid`

setuid and setgid are Unix access rights flags that allow users to run an executable with the permissions of the executable's owner or group respectively and to change behaviour in directories.

Using `/etc/skel` (skel = skeleton?)

The /etc/skel is a directory used by the command useradd to create the default settings in a new user's home directory.

roor@pc/etc/skel#ls -a
. .. .bashrc .profile

The settings for the command useradd can be changed by editing /etc/default/useradd

`wget` in windows

To get files available via http:

cmd > ps
:: in power shell is an alias for Invoke-WebRequest
wget https://www.example.com -OutFile out.html
:: for older PS versions
Invoke-WebRequest http://www.google.com/ -OutFile c:\google.html

As an alternative use curl, it needs to add more paramenters to control the output which does not goes to the a file with the same name as wget:

curl <url> -o <filename>

To act the same as wget, add {} to the URL to create the filename or the folder structure. e.g.:

curl http://example.com/{dir}/{file}.pdf -o '#1/#2.pdf'

This will create the file dir/file.pdf with the same name.

Which `tty` is being used:

To know which tty device is currently in use, use the command tty which returns the device being used.

As a side note is important for logging programs to check and adapt for the case in which the print output is a tty and when a file, this to take into account the buffering or pipe size. In the case of redirection with pipe the default size for a pipe named or not is 4k. If the buffer is not flushed some logs get lost in the pipe if not handled correctly.

Modify IO buffer in the terminal

The install command:

Install with non-sudo permisions in a / folder:

sudo install -d -o $(whoami) -g $(whoami) <folder_name>

Virtualization vs Containers

Create self cointained installation packages for linux/RH

Path too long in windows

There are at least 2 possiblities:

1. The command `subst`

This command creates a virtual drive with the given path:

subst z: b:\user\betty\forms :: creates the z: virtual drive pointing to c:\user\betty\forms
subst z: \d :: delete the virtual drive

2. The `\\?\`

https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx

`procfs` vs `sysfs`

sysfs was designed to add structure to sysproc and provide a uniform way to expose system information and control points to user-space from the kernel. Now, the driver framework in the kernel automatically creates directories under /sys when drivers are registered, based on the type and the values in their data structures.

procfs allowa arbitrary file_operations, sysfs is more restricted.
- `procfs receives a file_operations struct, which contains function pointers that determine what happens to every file-based system call (open, read, mmap)
While sysfs there is ony two methods show and store which linux uses to implement the open, close, read, write and lseek .

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