I'm using FreeBSD 7.3 (64 bit). When I try the command "cat /proc/self/maps", I get an error as, "cat: /proc/self/maps: No such file or directory". What should I do to resolve this ?
AFAIK, procfs isn't mounted by default in FreeBSD, so you should do it by yourself. Type as root:
mount -t procfs proc /proc
Or even better: add to /etc/fstab:
proc /proc procfs rw 0 0
Related
I have an embedded ARM system with processor AT91SAM9G45.
System consists of two components:
Linux kernel (4.14.79)
Busybox 1.29.3 as initramfs image.
I connect to the device using putty and connecting to serial port.
When kernel starts, everything goes fine. Kernel unpacks initramfs image, all files are found and listed (I see it by debug messages). But when it starts /init, log messages are:
Freeing unused kernel memory: 384K
This architecture does not have kernel memory protection.
run_init_process BEFORE /init
run_init_process AFTER /init, result = 0
Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
/init is symlink to /bin/busybox. I tried to replace /init with /sbin/init, /bin/busybox, /linuxrc, but results are the same.
/etc/inittab file:
# Begin /etc/inittab
id::initdefault:
si::sysinit:/etc/init.d/rc S
#l0::wait:/etc/rc.d/init.d/rc 0
#l1::wait:/etc/rc.d/init.d/rc 1
#l2::wait:/etc/rc.d/init.d/rc 2
#l3::wait:/etc/rc.d/init.d/rc 3
#l4::wait:/etc/rc.d/init.d/rc 4
#l5::wait:/etc/rc.d/init.d/rc 5
#l6::wait:/etc/rc.d/init.d/rc 6
ca::ctrlaltdel:/sbin/shutdown -t1 -a -r now
su::once:/sbin/sulogin
1::respawn:/sbin/getty ttyS1 115200
2::respawn:/sbin/getty ttyS2 115200
3::respawn:/sbin/getty ttyS3 115200
4::respawn:/sbin/getty ttyS4 115200
5::respawn:/sbin/getty ttyS5 115200
6::respawn:/sbin/getty ttyS6 115200
# End /etc/inittab
/etc/init.d/rcS file (this file is allowed to execute):
#!/bin/busybox sh
echo "Hello world!"
I don't know if even /init process starts parsing /etc/inittab or it falls before getting /etc/inittab by some reasons I cannot find out. Maybe there are
some mistakes in my /etc/inittab and /etc/init.d/rcS files. Maybe there are some errors with terminal (/etc/init.d/rcS cannot write to stdout cause it's blocked, suspended, being used by another process and so on).
How to definitely get sured, that /etc/inittab is started?
Welcome to StackOverflow.
I see there is space between rc and S
si::sysinit:/etc/init.d/rc S
change it to
si::sysinit:/etc/init.d/rcS
let me know if it works.
/init is symlink to /bin/busybox.
The typical /init file in an initramfs built by Buildroot that incorporates Busybox is a script of seven lines:
#!/bin/sh
# devtmpfs does not get automounted for initramfs
/bin/mount -t devtmpfs devtmpfs /dev
exec 0</dev/console
exec 1>/dev/console
exec 2>/dev/console
exec /sbin/init $*
Note the comment ("devtmpfs does not get automounted for initramfs") and the mount command for /dev.
It's /sbin/init (rather than /init) that is linked to /bin/busybox.
IOW without the proper setup of the /dev directory, userland has no I/O capabilty.
Only after devtmpfs has been mounted should the init program in Busybox be executed, which will then access /etc/inittab.
See Is there a way to get Linux to treat an initramfs as the final root filesystem?
and
Make CONFIG_DEVTMPFS_MOUNT apply to initramfs/initmpfs
I was trying to execute qemu while following the qemu/linaro tutorial,
https://developer.mozilla.org/en-US/docs/Mozilla/Developer_guide/Virtual_ARM_Linux_environment
I was executing the command,
sudo mount -o loop,offset=106496 -t auto vexpress.img /mnt/tmp
mount: you must specify the filesystem type
so i did fdisk on the img file and got the following,
Device Boot Start End Blocks Id System
vexpress.img1 * 63 106494 53216 e W95 FAT16 (LBA)
vexpress.img2 106496 6291455 3092480 83 Linux
The filesystem is Linux according to the fdisk command. But I get error,
sudo mount -o loop,offset=106496 -t Linux vexpress.img /mnt/tmp
mount: unknown filesystem type 'Linux'
Kindly help.
You correctly decide to mount the particular partition by specifying its offset but the offset parameter is in bytes and fdisk shows the offset in blocks (the block size is shown before the partition list --- usually 512). For the block size 512 the command would be:
sudo mount -o loop,offset=$((106496*512)) -t auto vexpress.img /mnt/tmp
If the automatic file system type detection does not still work there is another problem. Linux is not really a file system type. In the partition table it is a collective type used for multiple possible particular file systems. For mount you must specify the particular file system. In Linux you can list the supported ones by cat /proc/filesystems.
One of the books on advanced linux programming states:
The /proc/filesystems entry displays the file system types known to the kernel. Note that this list isn't very useful because it is not complete: File systems can be loaded and unloaded dynamically as kernel modules.The contents of /proc/filesystems list only file system types that either are statically linked into the kernel or are currently loaded. Other file system types may be available on the system as modules but might not be loaded yet.
Now, I have:
➜ ~ ps -C sshfs
PID TTY TIME CMD
8123 ? 00:00:00 sshfs
➜ ~ mount | grep sshfs
root#ss1: on /home/wani/tmp type fuse.sshfs (rw,nosuid,nodev,relatime,user_id=0,group_id=0)
➜ ~
But ...
➜ ~ cat /proc/filesystems | grep sshfs
➜ ~
sshfs is implemented in userspace using the FUSE infrastructure. Userspace filesystems are not known to the kernel as a separate entity. The FUSE kernel-side infrastructure itself, however, is known to the kernel. On my system:
$ cat /proc/filesystems
nodev sysfs
nodev rootfs
nodev ramfs
...
ext4
cramfs
...
nodev fuse
nodev fusectl
...
Note the last two lines; the kernel is aware of a fuse filesystem, which is essentially an adapter interface that lets filesystem services to be provided by userspace processes.
I am getting this error when I try to mount my UBIFS filesytem:
mount -o remount,rw /config
UBIFS error (pid 1265): ubifs_parse_options: unrecognized mount option "relatime" or
missing value
The content of my fstab is :
root#drgos:~# cat /etc/fstab
# WARNING: this is an auto generated file, please use uci to set static filesystems
/dev/ubi0_0 /config ubifs ro 0 0
And when I type mount the result is :
root#drgos:~# mount
rootfs on / type rootfs (rw)
none on /proc type proc (rw,relatime)
none on /sys type sysfs (rw,relatime)
tmpfs on /dev type tmpfs (rw,relatime,size=512k)
none on /dev/pts type devpts (rw,relatime,mode=600)
/dev/ubi0_0 on /config type ubifs (ro,relatime)
none on /proc/bus/usb type usbfs (rw,relatime)
I do not understand why I have the option relatime since that one is not present in my fstab!
I am using BusyBox v1.11.2 (2014-01-13 09:35:41 CET) multi-call binary.
These options are dependent on the Linux kernel version. relatime is a general mount options. relatime is the default for newer Linux kernels. Other filesystems may quietly ignore unknown options, whereas ubifs is failing. You can try mount -o remount,rw,noatime,norelatime /config. Your mount command shows the /config directory is mounted with relatime; this is information that busybox mount applet collected.
This information is collected with the getmntent_r() function. If busybox is dynamically linked, then the 'C' library may be giving this information as part of the *mnt_opts* string.
The idea with mount -o remount,rw,noatime,norelatime /config is to try and over-ride this information so that UbiFs will be happy with its mount options. The other way is to simply umount and then mount again manually.
umount /config
mount -t ubifs /dev/ubi0_0 /config
This way previous mount information will not be retrieved.
How can one detect being in a chroot jail without root privileges? Assume a standard BSD or Linux system. The best I came up with was to look at the inode value for "/" and to consider whether it is reasonably low, but I would like a more accurate method for detection.
[edit 20080916 142430 EST] Simply looking around the filesystem isn't sufficient, as it's not difficult to duplicate things like /boot and /dev to fool the jailed user.
[edit 20080916 142950 EST] For Linux systems, checking for unexpected values within /proc is reasonable, but what about systems that don't support /proc in the first place?
The inode for / will always be 2 if it's the root directory of an ext2/ext3/ext4 filesystem, but you may be chrooted inside a complete filesystem. If it's just chroot (and not some other virtualization), you could run mount and compare the mounted filesystems against what you see. Verify that every mount point has inode 2.
On Linux with root permissions, test if the root directory of the init process is your root directory. Although /proc/1/root is always a symbolic link to /, following it leads to the “master” root directory (assuming the init process is not chrooted, but that's hardly ever done). If /proc isn't mounted, you can bet you're in a chroot.
[ "$(stat -c %d:%i /)" != "$(stat -c %d:%i /proc/1/root/.)" ]
# With ash/bash/ksh/zsh
! [ -x /proc/1/root/. ] || [ /proc/1/root/. -ef / ]
This is more precise than looking at /proc/1/exe because that could be different outside a chroot if init has been upgraded since the last boot or if the chroot is on the main root filesystem and init is hard linked in it.
If you do not have root permissions, you can look at /proc/1/mountinfo and /proc/$$/mountinfo (briefly documented in filesystems/proc.txt in the Linux kernel documentation). This file is world-readable and contains a lot of information about each mount point in the process's view of the filesystem. The paths in that file are restricted by the chroot affecting the reader process, if any. If the process reading /proc/1/mountinfo is chrooted into a filesystem that's different from the global root (assuming pid 1's root is the global root), then no entry for / appears in /proc/1/mountinfo. If the process reading /proc/1/mountinfo is chrooted to a directory on the global root filesystem, then an entry for / appears in /proc/1/mountinfo, but with a different mount id. Incidentally, the root field ($4) indicates where the chroot is in its master filesystem. Again, this is specific to Linux.
[ "$(awk '$5=="/" {print $1}' </proc/1/mountinfo)" != "$(awk '$5=="/" {print $1}' </proc/$$/mountinfo)" ]
If you are not in a chroot and the root filesystem is ext2/ext3/ext4, the inode for / will always be 2. You may check that using
stat -c %i /
or
ls -id /
Interresting, but let's try to find path of chroot directory. Ask to stat on which device / is located:
stat -c %04D /
First byte is major of device and lest byte is minor. For example, 0802, means major 8, minor 1. If you check in /dev, you will see this device is /dev/sda2. If you are root you can directly create correspondong device in your chroot:
mknode /tmp/root_dev b 8 1
Now, let's find inode associated to our chroot. debugfs allows list contents of files using inode numbers. For exemple, ls -id / returned 923960:
sudo debugfs /tmp/root_dev -R 'ls <923960>'
923960 (12) . 915821 (32) .. 5636100 (12) var
5636319 (12) lib 5636322 (12) usr 5636345 (12) tmp
5636346 (12) sys 5636347 (12) sbin 5636348 (12) run
5636349 (12) root 5636350 (12) proc 5636351 (12) mnt
5636352 (12) home 5636353 (12) dev 5636354 (12) boot
5636355 (12) bin 5636356 (12) etc 5638152 (16) selinux
5769366 (12) srv 5769367 (12) opt 5769375 (3832) media
Interesting information is inode of .. entry: 915821. I can ask its content:
sudo debugfs /tmp/root_dev -R 'ls <915821>'
915821 (12) . 2 (12) .. 923960 (20) debian-jail
923961 (4052) other-jail
Directory called debian-jail has inode 923960. So last component of my chroot dir is debian-jail. Let's see parent directory (inode 2) now:
sudo debugfs /tmp/root_dev -R 'ls <2>'
2 (12) . 2 (12) .. 11 (20) lost+found 1046529 (12) home
130817 (12) etc 784897 (16) media 3603 (20) initrd.img
261633 (12) var 654081 (12) usr 392449 (12) sys 392450 (12) lib
784898 (12) root 915715 (12) sbin 1046530 (12) tmp
1046531 (12) bin 784899 (12) dev 392451 (12) mnt
915716 (12) run 12 (12) proc 1046532 (12) boot 13 (16) lib64
784945 (12) srv 915821 (12) opt 3604 (3796) vmlinuz
Directory called opt has inode 915821 and inode 2 is root of filesystem. So my chroot directory is /opt/debian-jail. Sure, /dev/sda1 may be mounted on another filesystem. You need to check that (use lsof or directly picking information /proc).
Preventing stuff like that is the whole point. If it's your code that's supposed to run in the chroot, have it set a flag on startup. If you're hacking, hack: check for several common things in known locations, count the files in /etc, something in /dev.
On BSD systems (check with uname -a), proc should always be present. Check if the dev/inode pair of /proc/1/exe (use stat on that path, it won't follow the symlink by text but by the underlying hook) matches /sbin/init.
Checking the root for inode #2 is also a good one.
On most other systems, a root user can find out much faster by attempting the fchdir root-breaking trick. If it goes anywhere you are in a chroot jail.
I guess it depends why you might be in a chroot, and whether any effort has gone into disguising it.
I'd check /proc, these files are automatically generated system information files. The kernel will populate these in the root filesystem, but it's possible that they don't exist in the chroot filesystem.
If the root filesystem's /proc has been bound to /proc in the chroot, then it is likely that there are some discrepancies between that information and the chroot environment. Check /proc/mounts for example.
Similrarly, check /sys.
I wanted the same information for a jail running on FreeBSD (as Ansible doesn't seem to detect this scenario).
On the FreeNAS distribution of FreeBSD 11, /proc is not mounted on the host, but it is within the jail. Whether this is also true on regular FreeBSD I don't know for sure, but procfs: Gone But Not Forgotten seems to suggest it is. Either way, you probably wouldn't want to try mounting it just to detect jail status and therefore I'm not certain it can be used as a reliable predictor of being within a jail.
I also ruled out using stat on / as certainly on FreeNAS all jails are given their own file system (i.e. a ZFS dataset) and therefore the / node on the host and in the jail both have inode 4. I expect this is common on FreeBSD 11 in general.
So the approach I settled on was using procstat on pid 0.
[root#host ~]# procstat 0
PID PPID PGID SID TSID THR LOGIN WCHAN EMUL COMM
0 0 0 0 0 1234 - swapin - kernel
[root#host ~]# echo $?
0
[root#host ~]# jexec guest tcsh
root#guest:/ # procstat 0
procstat: sysctl(kern.proc): No such process
procstat: procstat_getprocs()
root#guest:/ # echo $?
1
I am making an assumption here that pid 0 will always be the kernel on the host, and there won't be a pid 0 inside the jail.
If you entered the chroot with schroot, then you can check the value of $debian_chroot.