How do we reach ubi:rootfs_ubifs as we do with other /dev/* devices

[domic]

ubi:rootfs_ubifs

 

[ColinTaylor]

What do you mean by "reach"? Can you explain what it is you're trying to do.

It may vary depending on model and firmware but on my router ubi:rootfs_ubifs uses the character device /dev/ubi0_0, if that's what you're asking.

 

[Yota]

Enter df, then you will find it has been mounted as root /

 

[domic]

Enter df, then you will find it has been mounted as root /

That I know, but I'm confused as to why some folders in / or /tmp are persistent and some not across system reboots.
Everything under /tmp is traditionally a RAMdrive of sorts, at least back when I used OpenWRT on an old 4 MB flash, 32 MB RAM wifi router I used to have. /root gets wiped on reboot, yet /opt/* is kept etc but it's not part of /jffs from any ls -l I've done in the folders.
I must be missing something, because I managed to install something on /opt/* (part of / that didn't use up /jffs space and didn't show up as a /tmp/ folder either in ls -l lookups.

Heh, I'd like to understand the folder setup is setup, because my Linux knowledge can't figure out this stuff.

 

[ColinTaylor]

In the example below anything in tmpfs is not persistent. However quite a few other directories may be linked to /tmp, /var or some other storage device (e.g. USB) otherwise they wouldn't be able to be written to.

# df -h
Filesystem        Size  Used Avail Use% Mounted on
ubi:rootfs_ubifs   78M   74M  4.0M  95% /
devtmpfs          456M     0  456M   0% /dev
tmpfs             457M  1.1M  455M   1% /var
tmpfs             457M  1.3M  455M   1% /tmp
ubi1:data         4.5M   64K  4.2M   2% /data
/dev/mtdblock9     47M  3.8M   44M   8% /jffs
/dev/sda2          15G  5.7G  8.8G  40% /tmp/mnt/ClickUSB2
/dev/sda1          15G  4.5G  9.0G  34% /tmp/mnt/ClickUSB1

# ls -l /
drwxr-xr-x    2 admin    root          9800 Mar 25 15:12 bin
drwxr-xr-x    2 admin    root           160 Mar 25 15:12 cifs1
drwxr-xr-x    2 admin    root           160 Mar 25 15:12 cifs2
drwxr-xr-x    2 admin    root           392 Mar 25 17:58 data
lrwxrwxrwx    1 admin    root            16 Mar 25 15:12 debug -> sys/kernel/debug
drwxr-xr-x    5 admin    root          3640 Apr 25 22:33 dev
lrwxrwxrwx    1 admin    root             7 Mar 25 15:12 etc -> tmp/etc
lrwxrwxrwx    1 admin    root             8 Mar 25 15:12 home -> tmp/home
drwxr-xr-x   15 admin    root             0 Apr 28 23:11 jffs
drwxrwxr-x    5 admin    root          5584 Mar 25 15:12 lib
drwxrwxr-x    2 admin    root           384 Mar 25 15:12 lib64
drwxr-xr-x    2 admin    root           160 Mar 25 15:12 mmc
lrwxrwxrwx    1 admin    root             7 Mar 25 15:11 mnt -> tmp/mnt
lrwxrwxrwx    1 admin    root             7 Mar 25 15:12 opt -> tmp/opt
dr-xr-xr-x  173 admin    root             0 Jan  1  1970 proc
drwxr-xr-x    9 admin    root          2680 Mar 25 15:11 rom
lrwxrwxrwx    1 admin    root            13 Mar 25 15:12 root -> tmp/home/root
drwxr-xr-x    2 admin    root         12720 Mar 25 15:11 sbin
dr-xr-xr-x   12 admin    root             0 Jan  1  1970 sys
drwxr-xr-x    2 admin    root           160 Mar 25 15:12 sysroot
drwxrwxrwx   19 admin    root          1460 Apr 28 23:12 tmp
drwxr-xr-x   12 admin    root           880 Mar 25 15:12 usr
drwxrwxrwt   18 admin    root           460 Apr 28 23:08 var
drwxrwxr-x   16 admin    root         29832 Mar 25 15:12 www

So something like /root directs to /tmp/home/root:

admin@RT-AX86U:/# cd /root
admin@RT-AX86U:/tmp/home/root#

When Entware is installed on an external USB drive /opt is linked to it:

# ls -l /opt
lrwxrwxrwx    1 admin    root             7 Mar 25 15:12 /opt -> tmp/opt
# ls -l /tmp/opt
lrwxrwxrwx    1 admin    root            26 Apr 25 22:34 /tmp/opt -> /tmp/mnt/ClickUSB1/entware

 

[domic]

In the example below anything in tmpfs is not persistent. However quite a few other directories may be linked to /tmp, /var or some other storage device (e.g. USB) otherwise they wouldn't be able to be written to.

# df -h
Filesystem        Size  Used Avail Use% Mounted on
ubi:rootfs_ubifs   78M   74M  4.0M  95% /
devtmpfs          456M     0  456M   0% /dev
tmpfs             457M  1.1M  455M   1% /var
tmpfs             457M  1.3M  455M   1% /tmp
ubi1:data         4.5M   64K  4.2M   2% /data
/dev/mtdblock9     47M  3.8M   44M   8% /jffs
/dev/sda2          15G  5.7G  8.8G  40% /tmp/mnt/ClickUSB2
/dev/sda1          15G  4.5G  9.0G  34% /tmp/mnt/ClickUSB1

# ls -l /
drwxr-xr-x    2 admin    root          9800 Mar 25 15:12 bin
drwxr-xr-x    2 admin    root           160 Mar 25 15:12 cifs1
drwxr-xr-x    2 admin    root           160 Mar 25 15:12 cifs2
drwxr-xr-x    2 admin    root           392 Mar 25 17:58 data
lrwxrwxrwx    1 admin    root            16 Mar 25 15:12 debug -> sys/kernel/debug
drwxr-xr-x    5 admin    root          3640 Apr 25 22:33 dev
lrwxrwxrwx    1 admin    root             7 Mar 25 15:12 etc -> tmp/etc
lrwxrwxrwx    1 admin    root             8 Mar 25 15:12 home -> tmp/home
drwxr-xr-x   15 admin    root             0 Apr 28 23:11 jffs
drwxrwxr-x    5 admin    root          5584 Mar 25 15:12 lib
drwxrwxr-x    2 admin    root           384 Mar 25 15:12 lib64
drwxr-xr-x    2 admin    root           160 Mar 25 15:12 mmc
lrwxrwxrwx    1 admin    root             7 Mar 25 15:11 mnt -> tmp/mnt
lrwxrwxrwx    1 admin    root             7 Mar 25 15:12 opt -> tmp/opt
dr-xr-xr-x  173 admin    root             0 Jan  1  1970 proc
drwxr-xr-x    9 admin    root          2680 Mar 25 15:11 rom
lrwxrwxrwx    1 admin    root            13 Mar 25 15:12 root -> tmp/home/root
drwxr-xr-x    2 admin    root         12720 Mar 25 15:11 sbin
dr-xr-xr-x   12 admin    root             0 Jan  1  1970 sys
drwxr-xr-x    2 admin    root           160 Mar 25 15:12 sysroot
drwxrwxrwx   19 admin    root          1460 Apr 28 23:12 tmp
drwxr-xr-x   12 admin    root           880 Mar 25 15:12 usr
drwxrwxrwt   18 admin    root           460 Apr 28 23:08 var
drwxrwxr-x   16 admin    root         29832 Mar 25 15:12 www

So something like /root directs to /tmp/home/root:

admin@RT-AX86U:/# cd /root
admin@RT-AX86U:/tmp/home/root#

When Entware is installed on an external USB drive /opt is linked to it:

# ls -l /opt
lrwxrwxrwx    1 admin    root             7 Mar 25 15:12 /opt -> tmp/opt
# ls -l /tmp/opt
lrwxrwxrwx    1 admin    root            26 Apr 25 22:34 /tmp/opt -> /tmp/mnt/ClickUSB1/entware

Is there a Linux command that can output every jump of a symlink chain like THAT? Purpose would be to eliminate the headache of locating real paths or certain files or directories.
Example: /opt -> /tmp/opt -> /tmp/mnt/ClickUSB1

Or maybe a "list only symlinks in a tree style visual output that shows a branch of every recursive symlink etc."mount" and "df" commands sure don't tell the whole story by themselves.

Thank you for taking the time to answer my questions either way. I am very grateful.

 

[Crimliar]

So you are looking for a command like:
find ./ -type dl -print0 | xargs -0 ls -plah
?

 

[ColinTaylor]

Is there a Linux command that can output every jump of a symlink chain like THAT? Purpose would be to eliminate the headache of locating real paths or certain files or directories.
Example: /opt -> /tmp/opt -> /tmp/mnt/ClickUSB1

There is a command called realpath but it's not part of the firmware, although it can be added from Entware.

# opkg install coreutils-realpath
# realpath /opt
/tmp/mnt/ClickUSB1/entware

So you are looking for a command like:
find ./ -type dl -print0 | xargs -0 ls -plah
?

I don't think that works. -type dl is an invalid parameter.

You're probably thinking of something like this but the router's built-in version of find doesn't support -type at all (you'd need to install Entware's version):

# find / -path /proc -prune -o -path /sys -prune -o -type l -print0 | xargs -0 ls -lp | grep '/$'
lrwxrwxrwx    1 admin    root            16 Mar 25 15:12 /debug -> sys/kernel/debug/
lrwxrwxrwx    1 admin    root             7 Mar 25 15:12 /etc -> tmp/etc/
lrwxrwxrwx    1 admin    root             8 Mar 25 15:12 /home -> tmp/home/
lrwxrwxrwx    1 admin    root             7 Mar 25 15:11 /mnt -> tmp/mnt/
lrwxrwxrwx    1 admin    root             7 Mar 25 15:12 /opt -> tmp/opt/
lrwxrwxrwx    1 admin    root            13 Mar 25 15:12 /root -> tmp/home/root/
lrwxrwxrwx    1 admin    root            27 Apr 26 01:00 /tmp/diag_db_cloud/download/conn_diag_1650931200.db -> /tmp/diag_db_cloud/download/
lrwxrwxrwx    1 admin    root            27 Apr 27 01:00 /tmp/diag_db_cloud/download/conn_diag_1651017600.db -> /tmp/diag_db_cloud/download/
lrwxrwxrwx    1 admin    root            27 Apr 28 01:00 /tmp/diag_db_cloud/download/conn_diag_1651104000.db -> /tmp/diag_db_cloud/download/
lrwxrwxrwx    1 admin    root            27 Apr 29 01:00 /tmp/diag_db_cloud/download/conn_diag_1651190400.db -> /tmp/diag_db_cloud/download/
lrwxrwxrwx    1 admin    root            13 Jan  1  1970 /tmp/etc/adsl -> /rom/etc/adsl/
lrwxrwxrwx    1 admin    root            13 Jan  1  1970 /tmp/etc/dhcp -> /rom/etc/dhcp/
lrwxrwxrwx    1 admin    root            15 Jan  1  1970 /tmp/etc/init.d -> /rom/etc/init.d/
lrwxrwxrwx    1 admin    root            17 Jan  1  1970 /tmp/etc/iproute2 -> /rom/etc/iproute2/
lrwxrwxrwx    1 admin    root            12 Jan  1  1970 /tmp/etc/ppp -> /rom/etc/ppp/
lrwxrwxrwx    1 admin    root            14 Jan  1  1970 /tmp/etc/rc3.d -> /rom/etc/rc3.d/
lrwxrwxrwx    1 admin    root            12 Jan  1  1970 /tmp/etc/ssl -> /rom/etc/ssl/
lrwxrwxrwx    1 admin    root            12 Jan  1  1970 /tmp/etc/web -> /rom/etc/web/
lrwxrwxrwx    1 admin    root            13 Jan  1  1970 /tmp/etc/wlan -> /rom/etc/wlan/
lrwxrwxrwx    1 admin    root            26 Apr 25 22:34 /tmp/opt -> /tmp/mnt/ClickUSB1/entware/
lrwxrwxrwx    1 admin    root            10 Mar 25 15:12 /usr/local/share -> /tmp/share/
lrwxrwxrwx    1 admin    root            10 Mar 25 15:12 /usr/share/share -> /tmp/share/
lrwxrwxrwx    1 admin    root             6 Mar 25 15:12 /usr/tmp -> ../tmp/
lrwxrwxrwx    1 admin    root            15 Mar 25 15:12 /www/ext -> /tmp/var/wwwext/
lrwxrwxrwx    1 admin    root            15 Mar 25 15:12 /www/user -> /tmp/var/wwwext/