Q's Blog

iPhone ICCID Unlock: Activation Ticket Backup and Restore

2026-06-22T00:00:00+00:00
ICCID activation was once a common workaround for carrier-locked iPhones. Apple patched it, so it cannot issue new unlocked tickets, but tickets created before the patch still work. To preserve an existing unlock through a reset, downgrade, or DFU restore, back up the activation ticket first and restore it afterward. The ticket is tied to one device and cannot be transferred. I use my iPhone 5s (A1453, au/KDDI Japan) as the example.</p>
Recovering a Bricked 360T7 via UART After a DDR3 RAM Upgrade

2026-05-23T00:00:00+00:00
A memory-modded 360T7 had run for years until I flashed OpenWrt's bl2 and fip. It then stopped at dram size: 0MB</code>. Every rescue package I found failed for the same reason: OpenWrt's official bl2 drives DDR3 at 2133MT/s, while this router has a DDR3-1600 chip. DRAM initialization failed before the rest of the boot chain could load. I traced the settings in the ATF source, built a bl2 at 1866MT/s, and recovered the router over UART.</p>


Dual-Partition Sysupgrade on the 360V6 with OpenWrt
2026-05-23T00:00:00+00:00
The 360V6 has A/B dual-partition flash: two complete rootfs copies and a bootloader slot flag that selects one at boot. Updates write the inactive partition and leave the running one alone. If a write fails or is interrupted, the router can still boot the old system.</p>
OpenWrt's sysupgrade ignored the layout and wrote the running partition in place. A power loss or bad image mid-write left the device unbootable, recoverable only over TTL. I added proper A/B support upstream, and it has merged.</p>


Running BT and PT Behind CGNAT with WireGuard and a VPS
2024-11-11T19:52:11+00:00
BitTorrent and private-tracker clients benefit from accepting inbound connections, but CGNAT prevents that. Your ISP places multiple subscribers behind one public IPv4 address, so there is no inbound mapping for the home server. Port forwarding on the home router does not help because the relevant NAT is upstream at the ISP.</p>
A VPS with a public address and a WireGuard tunnel can relay the traffic. It receives torrent connections on a port range and forwards them through the tunnel to the home server. To peers, the home server is then reachable at the VPS's public address.</p>


Running Proxmox on a 2012 Mac Mini
2024-11-11T19:29:42+00:00
The Late 2012 Mac Mini Server makes a cheap Proxmox VE node and is the last fully upgradeable Mac Mini. Its two SO-DIMM slots support 16GB of RAM, and its two 2.5-inch SATA bays can hold a boot disk and a datastore. Apple soldered the RAM in 2014 and moved the line to ARM in 2020, so newer Minis either cannot take more memory or cannot run x86 virtualization.</p>
Its quad-core mobile Ivy Bridge i7 keeps power use modest for four cores. The whole machine is a 19cm-square box that fits on a shelf.</p>


Optimizing Sony Digital Paper for Chinese
2024-06-18T22:49:50+00:00
The Sony DPT-RP1 is a large-screen E Ink reader built for A4 PDFs. Sony ships the same firmware image in China, Japan, and the United States. A region identifier stored outside the firmware selects the UI language, the input methods, and the default font families, so flashing firmware cannot change the region.</p>
The Japanese build has Japanese and English fonts. The American build has English only, while the Chinese build has Chinese and English. My Japanese unit rendered Chinese characters in a book's table of contents with Japanese glyph variants, or did not render them at all. The Chinese and American builds did not have that problem. Their default font families differ.</p>


Surviving the OOM Killer with Swap
2024-01-13T03:27:26+00:00
The Linux OOM killer runs when the kernel can no longer reclaim memory. If anonymous memory exceeds RAM and has nowhere to go, the kernel scores processes and kills the one with the highest score. On a small VPS, that can be the application, database, or build job you meant to keep alive. A low-priority daemon with a large RSS can lose, but so can one large process when there is no swap.</p>
Swap gives anonymous pages backing storage under memory pressure. The kernel can evict those pages instead of killing the owning process, at the cost of latency when it reads them back. On a VPS, that delay is often preferable to losing the process.</p>


Converting .sas7bdat to CSV Without SAS
2023-08-27T15:16:21+00:00
.sas7bdat</code> is the binary format SAS uses to store data sets. SAS is commercial statistical software with a licensing cost that prices out most individual users. The format is proprietary and undocumented by SAS, so every reader outside it, including pyreadstat, is the product of reverse engineering.</p>
A single .sas7bdat</code> file holds the table itself, the column metadata, and enough type information to reconstruct rows. What it does not hold is the display layer. SAS stores human-readable value labels and formats in a separate catalog file, .sas7bcat</code>. Converting to CSV throws that layer away, because CSV has no place to put it.</p>


Creating a Bootable macOS USB Installer
2023-07-19T17:06:26+00:00
Making a macOS USB installer becomes awkward when the host and target use different architectures or macOS generations. I ran into it while reinstalling macOS 10.7 Lion on a 2012 Mac Pro from an M1 MacBook Air. The M1 cannot run Lion's installer, and Apple's direct Lion download is packaged in a form that modern macOS refuses to open.</p>


Disabling Automatic APT on a Low-Resource Debian VPS
2023-06-10T17:30:54+00:00
I run two inexpensive OranMe VPS instances: one has 0.1 CPU and 128MB RAM, the other 0.5 CPU and 512MB. They are only suitable for light self-hosted work, so I installed Debian without a desktop environment.</p>
The 0.1 CPU box kept shutting down. In the OranMe control panel, its CPU usage hit the limit shortly before each crash. That looked like the provider's abuse protection killing the VM. /var/log/system.log</code> showed that the spikes matched apt's periodic tasks.</p>


Setting Up an Nginx Web Server
2022-11-12T01:44:32-07:00
Nginx is an event-driven web server. Its worker pool multiplexes I/O across many connections instead of assigning a thread to each one. It is commonly used for static sites, reverse proxies, and TLS termination.</p>


Cell Phone Plans Worth Keeping and How to Get Them
2022-10-08T16:20:35-07:00
The cheapest cell plans in America are not advertised. They are grandfathered prepaid lines T-Mobile no longer sells, a $10/month unlimited tablet line, and a pay-per-use number you can keep alive for about a dollar a year.</p>


Building Padavan Router Firmware
2022-10-05T10:03:05-07:00
Padavan</a> is an open-source firmware derived from the GPL source ASUS released for the RT-N56U router. It targets MediaTek and Ralink SoCs: RT3883, MT7620, MT7621, and MT7628. The upstream repository on BitBucket last received updates in 2018. A fork on GitLab carries current development.</p>
A prebuilt image targets one board and feature set. Building from source lets you match the device and select the features to compile. This post builds firmware for the MI-NANO router, whose official firmware is old and has no IPv6 support.</p>


Kindle Jailbreaking: Unlocking Koreader and Custom Extensions
2022-10-02T12:17:25-07:00
Amazon's Kindle firmware locks you into the stock reader, which handles PDFs poorly and limits customization. Jailbreaking opens access to Koreader (a reader with PDF reflow and custom dictionaries), KUAL (a plugin launcher), and system-level tools like SSH. This guide covers the demo mode exploit for firmware 5.14.2 and earlier.</p>


Flashing the Xiaomi Router Nano Bootloader
2022-09-28T14:43:27-07:00
The Xiaomi Router Nano is a MediaTek MT7628 router. Stock MiWiFi accepts only signed updates and exposes no shell. Replacing the bootloader lets it run OpenWrt or Padavan.</p>


Remote LAN Access with ZeroTier, Tailscale, and Cloudflare Tunnel
2022-09-26T15:28:32-07:00
Remote LAN access lets devices reach a private network from anywhere. ZeroTier uses a virtual L2 network with P2P paths. Tailscale builds on WireGuard with NAT traversal. Cloudflare Tunnel uses a reverse proxy model.</p>


Linux System and Network Tuning
2022-07-28T15:02:35-07:00
Default Linux kernel parameters target general-purpose workloads. Servers handling high traffic, many connections, or heavy I/O need tuning. This guide covers the sysctl parameters that matter and why.</p>


Setting Up a Shadowsocks Proxy
2022-07-28T14:45:05-07:00
Shadowsocks-libev is an encrypted SOCKS5 proxy. It does not tunnel a whole network stack the way a VPN does. The client exposes a local SOCKS5 port that applications point at, and the server relays each connection to its destination over an encrypted link. The stream carries no recognizable protocol handshake, which is why it appears as random bytes to an observer. The usual topology puts the client behind a censoring network and the server on an overseas VPS.</p>
This post covers the libev implementation on Debian-family systems. The Chinese censor does more than watch traffic passively. It actively probes suspected servers, and a confirmed Shadowsocks server has its IP blocked in mainland China. Cipher choice determines how long a server lasts, not whether it is invulnerable.</p>


Free Certificates with Certbot
2022-07-18T17:12:32-07:00
ACME is the protocol for automated certificate management. Let's Encrypt speaks ACME. Certbot is the official ACME client from EFF. This guide covers Certbot with Cloudflare DNS validation.</p>


Setting Up a Trojan Proxy
2022-07-18T16:58:55-07:00
Trojan, from the trojan-gfw project, is a proxy protocol that uses TLS with a valid certificate on a real domain. Its traffic resembles ordinary HTTPS browsing.</p>
The server fronts a web server with ordinary content. A probe receives that website instead of a dead end.</p>


Array Algorithms
2022-07-12T12:25:04-07:00
Arrays store elements in contiguous memory. Access is O(1). Search and modification require iterating. This guide covers six algorithms that appear repeatedly in array problems: binary search, two pointers, sliding window, prefix sums, divide and conquer, and the Dutch national flag.</p>


Recursion and Iteration
2022-07-08T22:19:45-07:00
Recursion and iteration are interchangeable. Any loop can be rewritten as recursion, and any recursion can be rewritten as a loop using an explicit stack. The difference is cost. Recursion consumes the call stack and adds per-call overhead. Iteration does neither. The right choice depends on the problem structure and the language.</p>


Docker and Containers: Security, Rootless Mode, and Podman
2022-07-07T20:36:36-07:00
A container is not a virtual machine. VMs emulate hardware and run a full OS kernel. Containers share the host kernel and isolate processes using namespaces (which partition what a process sees: filesystem, network, PIDs, users) and cgroups (which cap what it uses: CPU, memory, I/O).</p>


Setting Up a Jekyll Blog
2022-07-06T16:29:28-07:00
Jekyll is a static site generator written in Ruby. It renders Markdown through Liquid templates into static HTML. The published site is a directory of files with no database and no server-side runtime at request time.</p>
On Apple Silicon, the Ruby toolchain needs a little setup first: Homebrew, a Ruby version manager, and the gem path.</p>


First Blog
2022-07-06T15:55:19-07:00

业精于勤荒于嬉，行成于思毁于随。

Achievements are reached by hard work rather than recreation. Actions are done after thorough consideration rather than casual decisions.</p>
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