Tmpfs
CLI reference:/disk
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.
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:
/disk/add type=tmpfs tmpfs-max-size=100M
[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:
/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:
/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:
[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:
[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:
/disk/set tmp1 smb-sharing=no media-sharing=no
Stop sharing new disks and folders automatically:
/disk/settings/set auto-smb-sharing=no auto-media-sharing=no
To share files on purpose, with your own users, see SMB and DLNA media server.
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.
/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:
/tool/sniffer/stop
Download tmp1/capture.pcap before the router reboots, with the Files menu in WinBox or WebFig (see Manage files in WinBox) or with scp from your computer:
scp admin@192.168.88.1:tmp1/capture.pcap .
For filters and live streaming, see 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:
[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:
/disk/set tmp1 tmpfs-max-size=200M
Delete the folder together with all files in it. RouterOS does not ask for confirmation:
/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:
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:
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.
For the parameters, see the /disk CLI reference.