# Tmpfs > A tmpfs is a folder in RAM for temporary files such as packet captures and downloads. Its size is capped, and its contents are lost on reboot. # Tmpfs A tmpfs is a folder in RAM. RouterOS shows it as a disk, for example `tmp1`, and files go into it like into any other disk. Use it for files that are needed only for a while and should not wear out or fill the flash: packet captures, files that a script downloads and imports, and other temporary files. Tmpfs is part of the base RouterOS package and works on every device that has the `/disk` menu, which SMIPS devices do not have. :::warning The contents of a tmpfs are lost when the router reboots or loses power. Copy the files you want to keep to the flash, a USB disk or a computer. ::: ## Create a RAM folder Add a folder that can hold up to 100 MB: ```ros /disk/add type=tmpfs tmpfs-max-size=100M ``` ```ros [admin@MikroTik] > /disk/print Flags: M - MOUNTED Columns: SLOT, MOUNT-POINT, MODEL, INTERFACE, SIZE, FREE, USE, FS # SLOT MOUNT-POINT MODEL INTERFACE SIZE FREE USE FS 0 M tmp1 tmp1 tmpfs ram 100 003 840 100 003 840 0% tmpfs ``` The first folder gets the slot name `tmp1`, the next one `tmp2`. The slot name is the start of the file path, for example `tmp1/capture.pcap`, and other commands refer to the folder by it. Sizes use decimal units: `100M` is 100 000 000 bytes. The size in `/disk/print` is rounded up to whole 4 KiB memory pages, so the folder shows 100 003 840. `tmpfs-max-size` is the most the folder can grow to; RAM is used only by the files stored in it. ## Check what the folder shares On routers whose default configuration turns on automatic disk sharing, a new tmpfs is shared as soon as it is created. Check the settings of your router first: ```ros /disk/settings/print ``` The default configuration of the hAP ax², for example, sets `auto-smb-sharing=yes`, `auto-media-sharing=yes` and `auto-media-interface=bridge`. The folder then gets an SMB share for the read-only `guest` user, who needs no password, and a DLNA media server on `bridge`. When `/ip/smb` is set to `enabled=auto`, the share also starts the SMB server. The SMB server listens on all interfaces (`interfaces=all`), and only the firewall limits who reaches it; the default firewall allows the LAN. Anyone who reaches the SMB server can read the files in the folder as `guest`, packet captures included, unless the `guest` user is disabled in `/ip/smb/users`. When automatic sharing is on, create the folder with sharing turned off. The setting stays after a reboot: ```ros /disk/add type=tmpfs tmpfs-max-size=100M smb-sharing=no media-sharing=no ``` The flags `s` (SMB sharing) and `m` (media sharing) in `/disk/print` show which folders are shared. Here `tmp1` was created with the automatic sharing and `tmp2` with the previous command: ```ros [admin@MikroTik] > /disk/print Flags: M - MOUNTED; s - SMB-SHARING; m - MEDIA-SHARING Columns: SLOT, MOUNT-POINT, MODEL, INTERFACE, SIZE, FREE, USE, FS # SLOT MOUNT-POINT MODEL INTERFACE SIZE FREE USE FS 0 Msm tmp1 tmp1 tmpfs ram 100 003 840 100 003 840 0% tmpfs 1 M tmp2 tmp2 tmpfs ram 100 003 840 100 003 840 0% tmpfs ``` The SMB share of a folder is a dynamic entry in `/ip/smb/shares`: ```ros [admin@MikroTik] > /ip/smb/shares/print Flags: D - DYNAMIC; X - DISABLED; * - DEFAULT Columns: NAME, DIRECTORY, REQUIRE-ENCRYPTION, VALID-USERS # NAME DIRECTORY REQUIRE-ENCRYPTION VALID-USERS 0 X* pub /pub no 1 D tmp1 /tmp1 no guest ``` Stop sharing a folder that is already shared: ```ros /disk/set tmp1 smb-sharing=no media-sharing=no ``` Stop sharing new disks and folders automatically: ```ros /disk/settings/set auto-smb-sharing=no auto-media-sharing=no ``` To share files on purpose, with your own users, see [SMB](smb) and [DLNA media server](dlna). ## Keep packet captures in RAM A packet capture can grow fast. Write it to the tmpfs instead of the flash, and keep `file-limit` (in KiB) below the folder size: `50000KiB` is about 51 MB, which fits in the 100 MB folder. ```ros /tool/sniffer/set file-name=tmp1/capture.pcap file-limit=50000KiB \ filter-interface=ether1 /tool/sniffer/start ``` Stop the capture when it has the packets you need: ```ros /tool/sniffer/stop ``` Download `tmp1/capture.pcap` before the router reboots, with the Files menu in WinBox or WebFig (see [Manage files in WinBox](../system-information-and-utilities/files#manage-files-in-winbox)) or with `scp` from your computer: ```bash scp admin@192.168.88.1:tmp1/capture.pcap . ``` For filters and live streaming, see [Packet sniffer](../diagnostics-monitoring-and-troubleshooting/packet-sniffer). ## Check how full the folder is The `FREE` and `USE` columns of `/disk/print` show how much of the folder is used. They update a few seconds after a write. List the files in the folder: ```ros [admin@MikroTik] > /file/print where name~"^tmp1" Columns: NAME, TYPE, SIZE, LAST-MODIFIED # NAME TYPE SIZE LAST-MODIFIED 0 tmp1 disk 2026-10-01 08:35:03 1 tmp1/capture.pcap .pcap file 19.8KiB 2026-10-01 08:35:08 ``` When the folder is full, writes to it fail. For example, `/tool/fetch` stops with `failure: cannot download: file too large, no space left on disk` and does not keep the partial file. ## Change the size or delete the folder A new size applies at once, also to a mounted folder: ```ros /disk/set tmp1 tmpfs-max-size=200M ``` Delete the folder together with all files in it. RouterOS does not ask for confirmation: ```ros /disk/remove tmp1 ``` ## Technical details ### Size limit Without `tmpfs-max-size` (it reads `0`), the folder can grow to about half of the router's RAM, for example 464 MB on a router with 1 GB of RAM. RouterOS adds up the maximum sizes of all tmpfs folders, counting a folder without `tmpfs-max-size` as half of the RAM, and refuses a new size when the total is more than the router can provide: ```text failure: too much memory requested for tmpfs/ramdisk ``` ### Memory use An empty tmpfs reserves no RAM. The files in it use RAM and lower `free-memory` in `/system/resource`. Files that fill the RAM can make the router run out of memory, so keep `tmpfs-max-size` well below the free memory. ### After a reboot The `/disk` entry and its settings stay in the configuration. After a reboot, RouterOS mounts the folder again under the same slot name, empty. Automatic SMB and DLNA shares of the folder come back with it, and a folder set to `smb-sharing=no` and `media-sharing=no` stays unshared. ### Not a block device A tmpfs is a file system, not a block device, so it cannot be formatted: ```text failure: cannot format nfs/smb/tmpfs/sshfs file systems ``` For RAM that works as a block device, for example as a RAID member, use a [Ramdisk](ramdisk). For the parameters, see the [`/disk` CLI reference](../cli-reference/disk/).