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Diffstat (limited to '3 Resources/Linux')
| -rw-r--r-- | 3 Resources/Linux/APT.md | 5 | ||||
| -rw-r--r-- | 3 Resources/Linux/Definitions.md | 6 | ||||
| -rw-r--r-- | 3 Resources/Linux/Device drivers.md | 22 | ||||
| -rw-r--r-- | 3 Resources/Linux/Device mapper.md | 28 | ||||
| -rw-r--r-- | 3 Resources/Linux/LSOF.md | 69 | ||||
| -rw-r--r-- | 3 Resources/Linux/PXE.md | 19 | ||||
| -rw-r--r-- | 3 Resources/Linux/Users.md | 22 | ||||
| -rw-r--r-- | 3 Resources/Linux/Watch.md | 4 | ||||
| -rw-r--r-- | 3 Resources/Linux/filesystems/Tmpfs.md | 16 |
9 files changed, 191 insertions, 0 deletions
diff --git a/3 Resources/Linux/APT.md b/3 Resources/Linux/APT.md new file mode 100644 index 0000000..9231d40 --- /dev/null +++ b/3 Resources/Linux/APT.md @@ -0,0 +1,5 @@ +#linux #packages #how-to + +--- +reinstall packages: +`apt reinstall <pkg>`
\ No newline at end of file diff --git a/3 Resources/Linux/Definitions.md b/3 Resources/Linux/Definitions.md new file mode 100644 index 0000000..c0ca4dd --- /dev/null +++ b/3 Resources/Linux/Definitions.md @@ -0,0 +1,6 @@ +#linux #definitions + +--- +NBP = Network Bootstrap Program +PXE = Preboot Execution Environment +NIC = Network Interface Card
\ No newline at end of file diff --git a/3 Resources/Linux/Device drivers.md b/3 Resources/Linux/Device drivers.md new file mode 100644 index 0000000..95f1a75 --- /dev/null +++ b/3 Resources/Linux/Device drivers.md @@ -0,0 +1,22 @@ +#linux #devices + +--- +major, minor numbers +major = driver (used by kernel when opening device to dispatch to correct driver) +minor = used by driver to differentiate device(s) + +after disk the major, minor numbers are shown: +``` +[jasras@n04.compute.vps2-lej1 ~]$ ls -l /dev/dm-* +brw-rw---- 1 root disk 253, 0 Oct 25 10:10 /dev/dm-0 +brw-rw---- 1 root disk 253, 1 Oct 25 10:11 /dev/dm-1 +brw-rw---- 1 root root 253, 11 Oct 28 19:58 /dev/dm-11 +brw-rw---- 1 root root 253, 12 Oct 28 19:58 /dev/dm-12 +``` + +available devices: `cat /proc/devices` + +character devices vs block devices; what is the difference? + +--- +[oreilly-device-drivers](https://www.oreilly.com/library/view/linux-device-drivers/0596000081/ch03s02.html)
\ No newline at end of file diff --git a/3 Resources/Linux/Device mapper.md b/3 Resources/Linux/Device mapper.md new file mode 100644 index 0000000..059a0d1 --- /dev/null +++ b/3 Resources/Linux/Device mapper.md @@ -0,0 +1,28 @@ +#linux #device-mapper + +--- +Device mapper is a kernel driver to map physical block devices to virtual ones; this means that for example we can have many physical devices be represented by a single virtual one (linear mapping). + +How does it work? +[[1 projects/Inwerken Mohammed/TODO]] +What is its function in relation to multipath? + +Logical devices using device-mapper can be managed using `man 8 dmsetup` +``` +[jasras@n04.compute.vps2-lej1 ~]$ sudo dmsetup info 3600a098038314d736724566a67346538 +Name: 3600a098038314d736724566a67346538 +State: ACTIVE +Read Ahead: 256 +Tables present: LIVE +Open count: 1 +Event number: 3 +Major, minor: 253, 12 +Number of targets: 1 +UUID: mpath-3600a098038314d736724566a67346538 +``` + +If dmsetup cannot remove a device because a process still has it open, but lsof does not show any processes that open it, use `-f` which replaces the device with a fake that rejects all I/O. + +--- +[device-mapper](https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/logical_volume_manager_administration/device_mapper#device_mapper) +[dmsetup](https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/logical_volume_manager_administration/dmsetup#dmsetup)
\ No newline at end of file diff --git a/3 Resources/Linux/LSOF.md b/3 Resources/Linux/LSOF.md new file mode 100644 index 0000000..5a3aa95 --- /dev/null +++ b/3 Resources/Linux/LSOF.md @@ -0,0 +1,69 @@ +#linux #how-to + +--- + +``` +lsof -p 1111 # show open files for this PID +lsof /path/to/file # show which process has this open +``` + +A usage in the wild; using lsof to find the qemu process for a specific base image and using that to get instance name and disk path: +``` +lsof -F p {{ item['path'] }} | cut -b 2- | head -1 | xargs ps | grep -oP '(instance\\-[a-z0-9]+)|(\\/var\\/lib\\/nova\\/instances\\/[a-z0-9\\-]+\\/disk)' | uniq +``` + +(man lsof: search "OUTPUT FOR OTHER PROGRAMS") +output for other programs +``` +specify -F +These are the fields that lsof will produce. The single character listed first is the field identifier. + a file access mode + c process command name (all characters from proc or + user structure) + C file structure share count + d file's device character code + D file's major/minor device number (0x<hexadecimal>) + f file descriptor (always selected) + F file structure address (0x<hexadecimal>) + G file flaGs (0x<hexadecimal>; names if +fg follows) + g process group ID + i file's inode number + K tasK ID + k link count + l file's lock status + L process login name + m marker between repeated output + M the task comMand name + n file name, comment, Internet address + N node identifier (ox<hexadecimal> + o file's offset (decimal) + p process ID (always selected) + P protocol name + r raw device number (0x<hexadecimal>) + R parent process ID + s file's size (decimal) + S file's stream identification + t file's type + T TCP/TPI information, identified by prefixes (the + `=' is part of the prefix): + QR=<read queue size> + QS=<send queue size> + SO=<socket options and values> (not all dialects) + SS=<socket states> (not all dialects) + ST=<connection state> + TF=<TCP flags and values> (not all dialects) + WR=<window read size> (not all dialects) + WW=<window write size> (not all dialects) + (TCP/TPI information isn't reported for all supported + UNIX dialects. The -h or -? help output for the + -T option will show what TCP/TPI reporting can be + requested.) + u process user ID + z Solaris 10 and higher zone name + Z SELinux security context (inhibited when SELinux is disabled) + 0 use NUL field terminator character in place of NL + 1-9 dialect-specific field identifiers (The output + of -F? identifies the information to be found + in dialect-specific fields.) + +```
\ No newline at end of file diff --git a/3 Resources/Linux/PXE.md b/3 Resources/Linux/PXE.md new file mode 100644 index 0000000..dcd59e7 --- /dev/null +++ b/3 Resources/Linux/PXE.md @@ -0,0 +1,19 @@ +--- +tags: + - linux +--- +The NBP is a bootloader that is obtained via the network typically via [[TFTP]]. It handles setting up an environment in which an OS can run or install. For example, it displays a boot menu and downloads the kernel images. It sets up hardware, for example the [[NIC]]s. + +PXE boot process: +1. Modified [[DHCP]] request: request to include boot information (PXE boot request). +2. Process DHCP response which includes an IP address of [[TFTP]] server and filename of [[NBP]]. +3. Download NBP over TFTP. +4. NBP executes + 1. Loads additional stuff over network, like kernel images. + 2. Handles the boot menu +5. Kernel takes over boot process and potentially downloads additional files required to complete booting. + +Popular NBP's: +- PXELINUX +- iPXE +- GRUB2 diff --git a/3 Resources/Linux/Users.md b/3 Resources/Linux/Users.md new file mode 100644 index 0000000..885a7cc --- /dev/null +++ b/3 Resources/Linux/Users.md @@ -0,0 +1,22 @@ +#linux #user-management + +Change uid/gid of user +`usermod -u newnumber user` +`groupmod -g newnumber user` + +File permissions in homedir will be automatically updated; file perms outside home dir will not be automatically updated. + +Finding files of a specific user, and printing their uid/gid; +`sudo find / -user 4109 -printf '%p %u(%U) %g(%G)\n'` + +To change only the group: `chgrp`. + +Or using find to chmod/chgrp: +`sudo find / -user 4109 -group 4109 -exec chmod 998:998 {} \;` +`sudo find / -group 4109 -exec chgrp 998 {} \;` + +Dirty way to find "system users" (uid < 999) - note that this is not fool-proof, it also lists groups +`getent passwd | grep -oP '\b[0-9]{3}\b' | uniq | sort` + +--- +https://www.cyberciti.biz/faq/linux-change-user-group-uid-gid-for-all-owned-files/ diff --git a/3 Resources/Linux/Watch.md b/3 Resources/Linux/Watch.md new file mode 100644 index 0000000..0c167b7 --- /dev/null +++ b/3 Resources/Linux/Watch.md @@ -0,0 +1,4 @@ +#linux #how-to + +--- +`watch (1)` periodically executes the executable on argv. It can be used to reload the output of a command, like `sudo watch ovs-dpctl dump-flows` . diff --git a/3 Resources/Linux/filesystems/Tmpfs.md b/3 Resources/Linux/filesystems/Tmpfs.md new file mode 100644 index 0000000..b8fe839 --- /dev/null +++ b/3 Resources/Linux/filesystems/Tmpfs.md @@ -0,0 +1,16 @@ +#linux #filesystem + +--- +Is a [[virtual filesystem]] that is stored in memory; it uses both RAM and swap space. +> Kernel option: CONFIG_TMPFS + +`mount -t tmpfs source target` + +A tmpfs can only grow to 50% of RAM avail. unless overridden with size=nbytes mount option. +Only consumes RAM for actual usage. +Data is ephemeral/volatile. + +Mount stacking: mount over existing /tmp, to improve speed of apps using alot of tmp files, then unmount to delete data. + +Kernel uses tmpfs for [[system v shared memory]] and [[shared anonymous memory mappings]]. +`/dev/shm` or `/run/shm`: [[glibc]] of [[POSIX]] shared memory and [[POSIX]] semaphores.
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