WiFi unstable (crashes around every day) TL-WR841N v9

After some time connected WiFi devices do not have access to the internet anymore. This happened on older firmwares before, but much less frequent. A few days ago I flashed the latest stable build and now I get lost connections around every day and need to restart the router.

I suspect that I have maybe to many clients (around 16) and that there is some hardware limitation like free RAM that lets the WiFi crash. That would maybe explain the increase of that problem with newer firmwares, since they consume more resources.

Is this problem known / normal or rather a bug?

Also, is there a way to find the root of it like checking log files?

And lastly, can there anything be done to avoid it? Else I might looking into purchasing a different device.

This is a 4/32 device, that hardly can be used, especially with so many clients.
Most likely this is OOM issue.
Purchasing another device is the best solution.

I know, that is why I thought it might be a resource issue.

The thing is that it ran rather fine with older builds, at least better than now. So, is there a way to at least temporarily reduce memory usage? Also I'd like to trace down the root of this, normally I'd expect the WiFi to come up again. Do logs help?

You can install older release that consumes less RAM.
Logs won't help if rhe router freezes.

Have you read this?

https://openwrt.org/supported_devices/432_warning

I have this v9 device. It works well enough even on 19.07 branch with ath79 target. But it is used with up to 3 wireless clients.

I read the warning already and am aware of it.

Won't flashing older releases introduce security problems?

The router itself does not freeze, at least in the past it was possible to connect via LAN. Only WiFi seems to crash.

Yes, it will.

So look what is RAM usage then and see the log too.

Well, I thought about disabling not needed services or something like this.

So, RAM usage is currently:

Free 3072 kB / 27844 kB (11%)

The log seems to get deleted on reboot, so does not contain related information. Will have to wait until next time.

Are all clients connected? When you get the problem next time, check RAM.

Currently 9 clients are connected via WLAN, 3 are connected via LAN. There is one more device currently not connected via WLAN, but I think that are all my devices.

I will check the RAM next time, however I think that won't help much, since then the WLAN already crashed, which might free up the RAM.

My guess is RAM exhaustion. Removing/disabling LuCI and the web server may help until you get a new device. With 10-15 clients, it seems that device just isn’t suited for the task.

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Alright. Sad that the WiFi network does not automatically recover.

I will have a look when the problem occurs again, but probably you are right. So I created a new post looking for a more suitable device.

Might want to note there that you’re running 10-15 clients, what “cheap” means to you, and what your ISP connection speed is. (16/128 is really the minimum I’d buy new, with 128 NAND available, as well as 256 MB RAM preferred for dual, “ath10k” radios)

Thanks for the hint, will do that!

I don't thing that flash > 32 is really of need.

Agreed, it was that I don’t consider 8 MB of flash a good choice in the current market.

I just got the WiFi crash.

Login via LAN is possible. The Web Gui shows:

Memory

Total Available
5736 kB / 27844 kB (20%)

Free
3504 kB / 27844 kB (12%)

Buffered
2232 kB / 27844 kB (8%)

System log (crash happened around 22:30):

Thu Aug  1 22:00:32 2019 daemon.info odhcpd[849]: Using a RA lifetime of 0 seconds on br-lan
Thu Aug  1 22:07:37 2019 daemon.info odhcpd[849]: Using a RA lifetime of 0 seconds on br-lan
Thu Aug  1 22:14:35 2019 daemon.info odhcpd[849]: Using a RA lifetime of 0 seconds on br-lan
Thu Aug  1 22:16:45 2019 daemon.info hostapd: wlan0: STA fc:a6:67:c6:9f:af IEEE 802.11: authenticated
Thu Aug  1 22:16:45 2019 daemon.info hostapd: wlan0: STA fc:a6:67:c6:9f:af IEEE 802.11: associated (aid 10)
Thu Aug  1 22:16:46 2019 daemon.notice hostapd: wlan0: AP-STA-CONNECTED fc:a6:67:c6:9f:af
Thu Aug  1 22:16:46 2019 daemon.info hostapd: wlan0: STA fc:a6:67:c6:9f:af WPA: pairwise key handshake completed (RSN)
Thu Aug  1 22:16:47 2019 daemon.info dnsmasq-dhcp[1397]: DHCPDISCOVER(br-lan) fc:a6:67:c6:9f:af
Thu Aug  1 22:16:47 2019 daemon.info dnsmasq-dhcp[1397]: DHCPOFFER(br-lan) 192.168.1.112 fc:a6:67:c6:9f:af
Thu Aug  1 22:16:47 2019 daemon.info dnsmasq-dhcp[1397]: DHCPREQUEST(br-lan) 192.168.1.112 fc:a6:67:c6:9f:af
Thu Aug  1 22:16:47 2019 daemon.info dnsmasq-dhcp[1397]: DHCPACK(br-lan) 192.168.1.112 fc:a6:67:c6:9f:af fire-tv-stick
Thu Aug  1 22:16:48 2019 daemon.info odhcpd[849]: Using a RA lifetime of 0 seconds on br-lan
Thu Aug  1 22:17:48 2019 daemon.info dnsmasq-dhcp[1397]: DHCPREQUEST(br-lan) 192.168.1.106 00:25:dc:ee:e1:32
Thu Aug  1 22:17:48 2019 daemon.info dnsmasq-dhcp[1397]: DHCPACK(br-lan) 192.168.1.106 00:25:dc:ee:e1:32 qivicon-home-base
Thu Aug  1 22:18:06 2019 daemon.info odhcpd[849]: Using a RA lifetime of 0 seconds on br-lan
Thu Aug  1 22:22:51 2019 daemon.info odhcpd[849]: Using a RA lifetime of 0 seconds on br-lan
Thu Aug  1 22:22:52 2019 daemon.info dnsmasq-dhcp[1397]: DHCPREQUEST(br-lan) 192.168.1.106 00:25:dc:ee:e1:32
Thu Aug  1 22:22:52 2019 daemon.info dnsmasq-dhcp[1397]: DHCPACK(br-lan) 192.168.1.106 00:25:dc:ee:e1:32 qivicon-home-base
Thu Aug  1 22:26:47 2019 daemon.info dnsmasq-dhcp[1397]: DHCPREQUEST(br-lan) 192.168.1.106 00:25:dc:ee:e1:32
Thu Aug  1 22:26:47 2019 daemon.info dnsmasq-dhcp[1397]: DHCPACK(br-lan) 192.168.1.106 00:25:dc:ee:e1:32 qivicon-home-base
Thu Aug  1 22:28:51 2019 daemon.info odhcpd[849]: Using a RA lifetime of 0 seconds on br-lan
Thu Aug  1 22:29:34 2019 daemon.info hostapd: wlan0: STA fc:a6:67:c6:9f:af IEEE 802.11: disconnected due to excessive missing ACKs
Thu Aug  1 22:29:34 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED fc:a6:67:c6:9f:af
Thu Aug  1 22:30:04 2019 daemon.info hostapd: wlan0: STA fc:a6:67:c6:9f:af IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
Thu Aug  1 22:31:16 2019 daemon.err uhttpd[904]: luci: accepted login on / for root from fdd5:24c4:abb4::e078:4761:e611:2310
Thu Aug  1 22:34:03 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED 40:31:3c:a4:6f:cb
Thu Aug  1 22:34:03 2019 daemon.info hostapd: wlan0: STA 40:31:3c:a4:6f:cb IEEE 802.11: disassociated due to inactivity
Thu Aug  1 22:34:04 2019 daemon.info hostapd: wlan0: STA 40:31:3c:a4:6f:cb IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
Thu Aug  1 22:34:15 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED 1c:12:b0:e0:93:0d
Thu Aug  1 22:34:15 2019 daemon.info hostapd: wlan0: STA 1c:12:b0:e0:93:0d IEEE 802.11: disassociated due to inactivity
Thu Aug  1 22:34:16 2019 daemon.info hostapd: wlan0: STA 1c:12:b0:e0:93:0d IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
Thu Aug  1 22:34:17 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED 3c:bd:3e:57:ee:c1
Thu Aug  1 22:34:17 2019 daemon.info hostapd: wlan0: STA 3c:bd:3e:57:ee:c1 IEEE 802.11: disassociated due to inactivity
Thu Aug  1 22:34:18 2019 daemon.info hostapd: wlan0: STA 3c:bd:3e:57:ee:c1 IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
Thu Aug  1 22:34:18 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED 7c:49:eb:15:66:bd
Thu Aug  1 22:34:18 2019 daemon.info hostapd: wlan0: STA 7c:49:eb:15:66:bd IEEE 802.11: disassociated due to inactivity
Thu Aug  1 22:34:19 2019 daemon.info hostapd: wlan0: STA 7c:49:eb:15:66:bd IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
Thu Aug  1 22:34:19 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED 68:54:fd:e6:c3:c8
Thu Aug  1 22:34:19 2019 daemon.info hostapd: wlan0: STA 68:54:fd:e6:c3:c8 IEEE 802.11: disassociated due to inactivity
Thu Aug  1 22:34:20 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED 5c:ff:ff:9f:2d:91
Thu Aug  1 22:34:20 2019 daemon.info hostapd: wlan0: STA 5c:ff:ff:9f:2d:91 IEEE 802.11: disassociated due to inactivity
Thu Aug  1 22:34:20 2019 daemon.info hostapd: wlan0: STA 68:54:fd:e6:c3:c8 IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
Thu Aug  1 22:34:21 2019 daemon.info hostapd: wlan0: STA 5c:ff:ff:9f:2d:91 IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
Thu Aug  1 22:34:28 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED 48:d6:d5:6a:85:66
Thu Aug  1 22:34:28 2019 daemon.info hostapd: wlan0: STA 48:d6:d5:6a:85:66 IEEE 802.11: disassociated due to inactivity
Thu Aug  1 22:34:29 2019 daemon.info hostapd: wlan0: STA 48:d6:d5:6a:85:66 IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
Thu Aug  1 22:34:31 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED f0:d7:aa:00:7e:9d
Thu Aug  1 22:34:31 2019 daemon.info hostapd: wlan0: STA f0:d7:aa:00:7e:9d IEEE 802.11: disassociated due to inactivity
Thu Aug  1 22:34:32 2019 daemon.info hostapd: wlan0: STA f0:d7:aa:00:7e:9d IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
Thu Aug  1 22:34:35 2019 daemon.notice hostapd: wlan0: AP-STA-DISCONNECTED 34:ea:34:f4:3c:42
Thu Aug  1 22:34:35 2019 daemon.info hostapd: wlan0: STA 34:ea:34:f4:3c:42 IEEE 802.11: disassociated due to inactivity
Thu Aug  1 22:34:36 2019 daemon.info hostapd: wlan0: STA 34:ea:34:f4:3c:42 IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)

Entire Kernel log (not sure whether anything relevant happened here, because there is no real timestamp):

[    0.000000] Linux version 4.9.184 (buildbot@2ccc8102e0c3) (gcc version 7.3.0 (OpenWrt GCC 7.3.0 r7808-ef686b7292) ) #0 Thu Jun 27 12:18:52 2019
[    0.000000] MyLoader: sysp=aaaba2aa, boardp=a2aaaaa2, parts=2aaa2a2a
[    0.000000] bootconsole [early0] enabled
[    0.000000] CPU0 revision is: 00019374 (MIPS 24Kc)
[    0.000000] SoC: Qualcomm Atheros QCA9533 ver 1 rev 1
[    0.000000] Determined physical RAM map:
[    0.000000]  memory: 02000000 @ 00000000 (usable)
[    0.000000] Initrd not found or empty - disabling initrd
[    0.000000] Primary instruction cache 64kB, VIPT, 4-way, linesize 32 bytes.
[    0.000000] Primary data cache 32kB, 4-way, VIPT, cache aliases, linesize 32 bytes
[    0.000000] Zone ranges:
[    0.000000]   Normal   [mem 0x0000000000000000-0x0000000001ffffff]
[    0.000000] Movable zone start for each node
[    0.000000] Early memory node ranges
[    0.000000]   node   0: [mem 0x0000000000000000-0x0000000001ffffff]
[    0.000000] Initmem setup node 0 [mem 0x0000000000000000-0x0000000001ffffff]
[    0.000000] On node 0 totalpages: 8192
[    0.000000] free_area_init_node: node 0, pgdat 80440ac4, node_mem_map 81000020
[    0.000000]   Normal zone: 64 pages used for memmap
[    0.000000]   Normal zone: 0 pages reserved
[    0.000000]   Normal zone: 8192 pages, LIFO batch:0
[    0.000000] pcpu-alloc: s0 r0 d32768 u32768 alloc=1*32768
[    0.000000] pcpu-alloc: [0] 0 
[    0.000000] Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 8128
[    0.000000] Kernel command line:  board=TL-WR841N-v9  console=ttyS0,115200 rootfstype=squashfs noinitrd
[    0.000000] PID hash table entries: 128 (order: -3, 512 bytes)
[    0.000000] Dentry cache hash table entries: 4096 (order: 2, 16384 bytes)
[    0.000000] Inode-cache hash table entries: 2048 (order: 1, 8192 bytes)
[    0.000000] Writing ErrCtl register=00000000
[    0.000000] Readback ErrCtl register=00000000
[    0.000000] Memory: 27604K/32768K available (3389K kernel code, 162K rwdata, 424K rodata, 240K init, 211K bss, 5164K reserved, 0K cma-reserved)
[    0.000000] SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
[    0.000000] NR_IRQS:51
[    0.000000] Clocks: CPU:550.000MHz, DDR:395.800MHz, AHB:197.900MHz, Ref:25.000MHz
[    0.000000] clocksource: MIPS: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 6950037990 ns
[    0.000010] sched_clock: 32 bits at 275MHz, resolution 3ns, wraps every 7809031678ns
[    0.008274] Calibrating delay loop... 366.18 BogoMIPS (lpj=1830912)
[    0.071070] pid_max: default: 32768 minimum: 301
[    0.076075] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
[    0.083063] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
[    0.093839] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
[    0.104265] futex hash table entries: 256 (order: -1, 3072 bytes)
[    0.112200] NET: Registered protocol family 16
[    0.118661] MIPS: machine is TP-LINK TL-WR841N/ND v9
[    0.614346] clocksource: Switched to clocksource MIPS
[    0.620969] NET: Registered protocol family 2
[    0.626708] TCP established hash table entries: 1024 (order: 0, 4096 bytes)
[    0.634071] TCP bind hash table entries: 1024 (order: 0, 4096 bytes)
[    0.640848] TCP: Hash tables configured (established 1024 bind 1024)
[    0.647698] UDP hash table entries: 256 (order: 0, 4096 bytes)
[    0.653876] UDP-Lite hash table entries: 256 (order: 0, 4096 bytes)
[    0.660844] NET: Registered protocol family 1
[    0.665520] PCI: CLS 0 bytes, default 32
[    0.669767] Crashlog allocated RAM at address 0x1f00000
[    0.676720] workingset: timestamp_bits=30 max_order=13 bucket_order=0
[    0.691427] squashfs: version 4.0 (2009/01/31) Phillip Lougher
[    0.697629] jffs2: version 2.2 (NAND) (SUMMARY) (LZMA) (RTIME) (CMODE_PRIORITY) (c) 2001-2006 Red Hat, Inc.
[    0.719014] io scheduler noop registered
[    0.723152] io scheduler deadline registered (default)
[    0.729116] Serial: 8250/16550 driver, 16 ports, IRQ sharing enabled
[    0.738909] console [ttyS0] disabled
[    0.762857] serial8250.0: ttyS0 at MMIO 0x18020000 (irq = 11, base_baud = 1562500) is a 16550A
[    0.771974] console [ttyS0] enabled
[    0.779540] bootconsole [early0] disabled
[    0.795431] m25p80 spi0.0: found s25sl032p, expected m25p80
[    0.801217] m25p80 spi0.0: s25sl032p (4096 Kbytes)
[    0.807149] 5 tp-link partitions found on MTD device spi0.0
[    0.812916] Creating 5 MTD partitions on "spi0.0":
[    0.817934] 0x000000000000-0x000000020000 : "u-boot"
[    0.825422] 0x000000020000-0x00000016babc : "kernel"
[    0.832952] 0x00000016babc-0x0000003f0000 : "rootfs"
[    0.840019] mtd: device 2 (rootfs) set to be root filesystem
[    0.846007] 1 squashfs-split partitions found on MTD device rootfs
[    0.852398] 0x0000003a0000-0x0000003f0000 : "rootfs_data"
[    0.860553] 0x0000003f0000-0x000000400000 : "art"
[    0.867900] 0x000000020000-0x0000003f0000 : "firmware"
[    0.876841] libphy: Fixed MDIO Bus: probed
[    0.906899] libphy: ag71xx_mdio: probed
[    1.536909] ag71xx-mdio.1: Found an AR934X built-in switch
[    1.590359] eth0: Atheros AG71xx at 0xba000000, irq 5, mode:GMII
[    2.227319] ag71xx ag71xx.0: connected to PHY at ag71xx-mdio.1:04 [uid=004dd042, driver=Generic PHY]
[    2.237626] eth1: Atheros AG71xx at 0xb9000000, irq 4, mode:MII
[    2.246303] NET: Registered protocol family 10
[    2.256180] NET: Registered protocol family 17
[    2.260840] bridge: filtering via arp/ip/ip6tables is no longer available by default. Update your scripts to load br_netfilter if you need this.
[    2.274418] 8021q: 802.1Q VLAN Support v1.8
[    2.280825] hctosys: unable to open rtc device (rtc0)
[    2.291491] VFS: Mounted root (squashfs filesystem) readonly on device 31:2.
[    2.300486] Freeing unused kernel memory: 240K
[    2.305117] This architecture does not have kernel memory protection.
[    2.534402] random: fast init done
[    3.036909] init: Console is alive
[    3.040701] init: - watchdog -
[    3.955214] kmodloader: loading kernel modules from /etc/modules-boot.d/*
[    4.015124] kmodloader: done loading kernel modules from /etc/modules-boot.d/*
[    4.033524] init: - preinit -
[    4.822752] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
[    4.854021] random: procd: uninitialized urandom read (4 bytes read)
[    6.455796] eth0: link up (1000Mbps/Full duplex)
[    6.460611] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[    8.154188] jffs2: notice: (401) jffs2_build_xattr_subsystem: complete building xattr subsystem, 0 of xdatum (0 unchecked, 0 orphan) and 0 of xref (0 dead, 0 orphan) found.
[    8.171832] mount_root: switching to jffs2 overlay
[    8.215749] urandom-seed: Seeding with /etc/urandom.seed
[    8.421336] eth0: link down
[    8.438610] procd: - early -
[    8.441717] procd: - watchdog -
[    9.082657] procd: - watchdog -
[    9.086372] procd: - ubus -
[    9.199434] random: ubusd: uninitialized urandom read (4 bytes read)
[    9.208936] random: ubusd: uninitialized urandom read (4 bytes read)
[    9.216118] random: ubusd: uninitialized urandom read (4 bytes read)
[    9.223686] procd: - init -
[    9.648216] kmodloader: loading kernel modules from /etc/modules.d/*
[    9.660002] ip6_tables: (C) 2000-2006 Netfilter Core Team
[    9.678493] Loading modules backported from Linux version wt-2017-11-01-0-gfe248fc2c180
[    9.686850] Backport generated by backports.git v4.14-rc2-1-31-g86cf0e5d
[    9.697430] ip_tables: (C) 2000-2006 Netfilter Core Team
[    9.712666] nf_conntrack version 0.5.0 (1024 buckets, 4096 max)
[    9.781873] xt_time: kernel timezone is -0000
[    9.846352] PPP generic driver version 2.4.2
[    9.853706] NET: Registered protocol family 24
[    9.904147] ath: EEPROM regdomain: 0x0
[    9.904159] ath: EEPROM indicates default country code should be used
[    9.904163] ath: doing EEPROM country->regdmn map search
[    9.904182] ath: country maps to regdmn code: 0x3a
[    9.904188] ath: Country alpha2 being used: US
[    9.904192] ath: Regpair used: 0x3a
[    9.916189] ieee80211 phy0: Selected rate control algorithm 'minstrel_ht'
[    9.921223] ieee80211 phy0: Atheros AR9531 Rev:1 mem=0xb8100000, irq=47
[   10.045790] kmodloader: done loading kernel modules from /etc/modules.d/*
[   11.207728] urandom_read: 5 callbacks suppressed
[   11.207738] random: jshn: uninitialized urandom read (4 bytes read)
[   21.940359] br-lan: port 1(eth0) entered blocking state
[   21.945846] br-lan: port 1(eth0) entered disabled state
[   21.951695] device eth0 entered promiscuous mode
[   22.039213] IPv6: ADDRCONF(NETDEV_UP): br-lan: link is not ready
[   22.109178] IPv6: ADDRCONF(NETDEV_UP): eth1: link is not ready
[   23.573474] eth0: link up (1000Mbps/Full duplex)
[   23.671762] br-lan: port 1(eth0) entered blocking state
[   23.677245] br-lan: port 1(eth0) entered forwarding state
[   23.754438] IPv6: ADDRCONF(NETDEV_CHANGE): br-lan: link becomes ready
[   24.227233] eth1: link up (100Mbps/Full duplex)
[   24.274508] IPv6: ADDRCONF(NETDEV_CHANGE): eth1: link becomes ready
[   24.356682] ath: EEPROM regdomain: 0x8114
[   24.360838] ath: EEPROM indicates we should expect a country code
[   24.367206] ath: doing EEPROM country->regdmn map search
[   24.372690] ath: country maps to regdmn code: 0x37
[   24.377654] ath: Country alpha2 being used: DE
[   24.382240] ath: Regpair used: 0x37
[   24.385859] ath: regdomain 0x8114 dynamically updated by user
[   27.395802] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[   27.498877] br-lan: port 2(wlan0) entered blocking state
[   27.504464] br-lan: port 2(wlan0) entered disabled state
[   27.510437] device wlan0 entered promiscuous mode
[   28.228312] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
[   28.235326] br-lan: port 2(wlan0) entered blocking state
[   28.240852] br-lan: port 2(wlan0) entered forwarding state
[   49.106789] random: crng init done

Do you see anything that might give a clue on what has happened?

Assuming you logged in just prior to the crash, from this entry

https://openwrt.org/toh/tp-link/tl-wr841nd -- v9: 32 MB RAM

https://openwrt.org/supported_devices/432_warning

32 MB can work for minimal router/AP functions, but may repeatedly “crash”, depending on your hardware and use case

Looking at RAM consumption after the crash isn't going to reveal that that you've run out just prior to the crash.


Edit:

One way to "watch" the memory usage would be open a terminal session (so that it's in the scrollback if the router crashes) and run something like

while printf "%s\t%s\n" "$(date)" "$(free | head -n2 | tail -n1)" ; do sleep 1 ; done

Ah, did not notice the login entry. In fact I logged in just after the crash, not before.

I thought the same, but it was suggested to do so, so I did. I guess the log might offer more relevant details.

This are the log entries just before the "crash". I think it is what caused it or at least the symptoms of it. I had a short Google search and there have been similar problems with disconnects "due to excessive missing ACKs" on other router models, but not sure whether this is the same problem here or has a different root.

Sorry, but no.
Logs do not survive crash & reboot, as logs are held in RAM in order to avoid flash writes. You will not get any useful information from new logs, which are totally about after-reboot events.

The timestamp that misleads you, is wrong. Your router has no real time clock, so it loses time after reboot. The router uses the date/time of the most recent file on /etc as an approximation of the best known last date/time before the router can update NTP time from internet. So after reboot the timestamps in the log are wrong... If you look closer at the system log, there is usually a gap/jump in time when it gets refreshed.

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