In Linux account administration, a UID range is a contiguous span of numeric user IDs available for assigning identities. The numbers are not governed by one universal rule: conventions depend on the Linux distribution and version, while centralized identity systems can configure ranges to prevent conflicts across their environment. “UID range” also has separate meanings in Android networking code and IEEE identifier standards, so the right interpretation depends on context.
What a UID range means in Linux
A Linux user identifier (UID) is a number associated with a user account. A UID range is an interval of such numbers—for example, a system may reserve one span for system accounts and another for ordinary users. The range describes which identifiers may be allocated; it does not, by itself, create accounts or guarantee that two separate systems assign the same person the same UID.
UIDs matter because Linux uses numeric identities when applying ownership and access permissions. In a standalone installation, local account-management conventions determine how IDs are assigned. In a centrally managed environment, administrators may configure ranges so that users and groups receive consistent, non-conflicting IDs across clients.
Which Linux UID range should be used?
Historical LSB allocation guidance
The Linux Standard Base (LSB) 2.0.1 specification says that system UIDs 0–99 “should be statically allocated by the system, and shall not be created by applications.” It also says UIDs 100–499 should be reserved for dynamic allocation by system administrators and post-installation scripts using useradd. These are the LSB 2.0.1 specification’s allocation rules, not universal current defaults for every Linux distribution. See the Linux Foundation LSB 2.0.1 UID range specification.
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Current distribution settings
Do not assume that those historical boundaries match the defaults on a current installation. Distributions can set their own ranges, and the relevant configuration depends on the distribution and its version. Before creating system or service accounts, check the documentation and account-allocation settings for the exact system you administer. The cited LSB rule is useful as a named historical standard, not as a substitute for that check.
How UID ranges help prevent conflicts in centralized identity management
In Red Hat Enterprise Linux 8 Identity Management (IdM), ID ranges define valid UID and GID values for users, hosts, and groups in an IdM topology. Red Hat describes range assignment as a way to avoid ID conflicts and provide consistent IDs across clients. This is guidance specific to RHEL 8 IdM; it should not be treated as a universal configuration rule for all Linux identity systems. Details are in Red Hat’s RHEL 8 Identity Management planning documentation.
The operational point is scope: a range must be considered alongside the other identities that may appear in the same managed environment. If separate authorities can allocate overlapping IDs, two distinct accounts may be represented by the same numeric identity on a client. A range plan should therefore be coordinated across the relevant identity sources and clients rather than chosen independently on each machine.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.UID ranges in Linux, Android, and IEEE terminology
| Context | What the identifier refers to | How the range is used | Scope or qualification |
|---|---|---|---|
| Linux account administration | A user account’s numeric UID | Allocation conventions or configured identity-management intervals | Distribution, version, and management system determine applicable rules. |
| Android network policy | UID values handled by Android’s netd networking component |
Code accepts one UID or a start–stop interval, rejects reversed intervals, and treats ranges as overlapping when they share any UID | Behavior shown in Android source tag android-15.0.0_r23; this is not Linux account-allocation policy. |
| IEEE EUI identifiers | Extended Unique Identifier (EUI) blocks, not Linux user accounts | MA-L, MA-M, and MA-S refer to different block sizes for EUI identifiers | A separate identifier family; it should not be confused with a Linux UID range. |
For the Android interval behavior, see the Android netd source for android-15.0.0_r23. For the distinct IEEE terminology, see the IEEE guidance on EUI, OUI, and CID identifiers.
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How to avoid UID conflicts across Linux systems
- Identify the management model. Determine whether accounts are local to each machine or managed through a shared identity service.
- Check the actual allocation policy. Use documentation and configuration for the relevant distribution, version, and identity-management product; do not infer current defaults from LSB 2.0.1.
- Coordinate the allocation space. In a centralized topology, assign ranges so the identities managed by the participating authorities do not collide, and use the system’s documented mechanism to keep IDs consistent across clients.
- Keep platform-specific meanings separate. Android network-policy UID intervals and IEEE EUI blocks are not Linux account ranges and should not be used to select Linux account IDs.
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