From 03b4be77e50c01cd0463089e68bbe673362a897b Mon Sep 17 00:00:00 2001 From: johannst Date: Mon, 29 Aug 2022 20:27:58 +0000 Subject: deploy: 8de64474ded169db55cdd34be9c020ed13c4e5e7 --- print.html | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 76 insertions(+), 1 deletion(-) (limited to 'print.html') diff --git a/print.html b/print.html index 10d3605..8de9266 100644 --- a/print.html +++ b/print.html @@ -76,7 +76,7 @@ @@ -2641,6 +2641,8 @@ gcc -march=native -Q --help=target

Give the compiler a hint which branch is hot, so it can lay out the code accordingly to reduce number of jump instructions. See on compiler explorer.

+

The semantics of this hint are as follows, the compiler prioritises expr == cond. So __builtin_expect(expr, 0) means that we expect the expr to be 0 +most of the time.

echo "
 extern void foo();
 extern void bar();
@@ -3189,6 +3191,7 @@ def sum(a: int, b: int) -> int:
 
  • systemd
    • 
 
  • coredump
    • 
 
  • ptrace_scope
    • 
+
  • cryptsetup
    • 
 
 
    systemd
    
 
    systemctl
    
@@ -3337,6 +3340,78 @@ coredumpctl dump 6363 -o <file>
     3 => No tracing allowed.

    Further details in ptrace(2).

    +

    cryptsetup(8)

    +
    cryptsetup <action> [opts] <action args>
+
+action:
+    open <dev> <name> --type <type>    Open (decrypt) <dev> and map with <name>.
+                                       Mapped as /dev/mapper/<name>.
+                                       Type: {luks,plain,tcrypt,bitlk}
+    close <name>                       Close existing mapping <name>.
+    status <name>                      Print status for mapping <name>.
+
+    luksFormat <dev>                   Create new LUKS partition and set initial passphrase.
+                                       (Keyslot 0)
+    luksAddKey <dev>                   Add a new passphrase.
+    luksRemoveKey <dev>                Remove existing passphrase.
+    luksChangeKey <dev>                Change existing passphrase.
+    lusDump <dev>                      Dump LUKS header for device.
+
    +

    Example: Create LUKS encrypted disk.

    +

    For this example we use a file as backing storage and set it up as +loop(4) device. The loop device can be replaced by any block +device file.

    +
    +

    Optional: Overwrite existing data on disk.
    +sudo dd if=/dev/urandom of=/dev/sdX bs=1M

    +
    +

    First create the backing file and setup the loop device.

    +
    # Create 100MB file.
+dd if=/dev/zero of=blkfile bs=1M count=100
+
+# Attach file to first free (-f) loop device
+sudo losetup -f ./blkfile
+# List loop devices.
+sudo losetup -l
+# NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE              DIO LOG-SEC
+# /dev/loop0         0      0         0  0 /home/johannst/blkfile   0     512
+
    +

    Create a new LUKS partition and format new filesystem.

    +
    # Initialize LUKS partition and set initial passphrase.
+sudo cryptsetup luksFormat /dev/loop0
+
+file blkfile
+# blkfile: LUKS encrypted file, ver 2 [, , sha256] UUID: 8...
+
+# Open (decrypt) the LUKS device, it will be mapped under /dev/mapper/loop0.
+sudo cryptsetup open --type luks /dev/loop0 loop0
+
+# Format partition with new filesystem.
+sudo mkfs.vfat /dev/mapper/loop0
+
+lsblk -f
+# NAME        FSTYPE    FSVER LABEL  UUID  FSAVAIL FSUSE% MOUNTPOINTS
+# loop0       crypto_LU 2            8...
+# └─loop0     vfat      FAT16        D...    83.8M     0% /home/johannst/mnt
+
+# Close (re-encrypt) LUKS device.
+sudo cryptsetup close loop0
+
    +

    Example: Using an existing LUKS device.

    +
    # Open (decrypt) the LUKS device, it will be mapped under /dev/mapper/loop0.
+sudo cryptsetup open --type luks /dev/loop0 loop0
+
+# Mount filesystem.
+sudo mount /dev/mapper/loop0 <mntpoint>
+
+# Use disk ...
+
+# Unmount filesystem.
+sudo umount <mntpoint>
+
+# Close (re-encrypt) LUKS device.
+sudo cryptsetup close loop0
+

    Network